Even if prophecy were possible, it would be impossible.
This is because as soon as you know the future, you can't help but change the future by virtue of you knowing.
Imagine that you learn that you will meet the love of your life next Saturday, fall in love, and have six kids. This is a 100% true prophecy at the time at which it was made.
But then, that future will no longer come to pass because you have exited that timeline, by virtue of you knowing it. Suddenly, you are very conscious of where you were planning to go on Saturday. Your friends invited you to the city, were you going to go with them? Or were you going to stay home, and maybe just go to the grocery store? And should you get a haircut before you meet the love of your life?
Point is, you are no longer behaving like you were before you received the gift of prophecy. You are acting like a crazy person. And even if you do pick the right course of action (stay home) and meet the love of your life at the grocery store, you might still fuck it up by coming on too strong, being too shy, or not bringing a pen that you could lend out (because you were too busy getting a haircut)--all things that you wouldn't have done if you had been ignorant of your future.
By learning your future, you have changed it.
The quiet prophets are ones that allow themselves to be sealed inside tombs, where they quietly write out some cuniform prophecy and then die meekly in the darkness. As long as that prophecy doesn't leave that sealed chamber, it cannot change the future, and therefore invalidate itself. A prophecy is only "fresh" for as long as it remains unknown.
And hopefully, their tomb was marked with a scheduled date, so that the tomb could be opened at the appropriate time, where the prophecy is early enough to be of some use, but not so late the the knowledge of the prophecy spoils itself with knowledge.
But of course, the knowledge of the perfect time to open the tomb also requires prophecy, so any number chiseled on the outside will also have to be either a prophecy (which self-invalidates, as people will speculate on what that date portends, and therefore spoil the prophecy) or a guess. Both of which carry their own risks.
It's not that it's difficult to see the future, it's that it's so easy that anyone can do it.
Clerics of all stripes can see the future accurately. And many of them change their behavior based on the information they receive, which of course means that all previous prophecies are invalidated almost as quickly as they are written down.
You can make a prophecy about what will happen next Wednesday, but by Monday someone else will have made a prophecy themselves, altering the timeline, and rendering your prophecy null and void.
And so there are many dead prophets in tombs with worthless cuniform. This is the tragedy of the common timeline. It's like sharing a pool; everyone shits in it.
There have been attempts to regulate the timeline sso that all these trivial prophecies would clear the waters, allowing room for the big, useful propheciess (i.e. the temporal estates of the Elf Lords, or the One Future doctrine of the Church) but these all have ended in different forms of failure.
But what about prophecies that include the effects of the prophecy in the prophecy?
This is like finding out that you will meet the love of your life this weekend, and that fact gaining you the confidence you needed to talk to people of the opposite gender, which allows you to meet your future spouse. This would have been impossible if you weren't inspired by the original prophecy.
So although this prophecy seems to be accurate because it accounts for itself, it is also dependent on itself. You wouldn't have found love if you hadn't been prophecied to find love.
And so the prophecy becomes not just an indicator of the future, but a decider of the future instead.
And as any good prophet knows, the future is plastic. Sometimes multiple, mutually-exclusive futures can be possible. It's not uncommon for a fortune-teller to have a situation like this:
A farmer walks in an asks to know his future. If the fortune teller tells him that he will meet a new friend tomorrow, he will meet Marf the brewer and the two will become lifelong friends, since the farmer is expecting to meet a friend. If the fortune teller tells the farmer that he will meet a new enemy tomorrow, the farmer will meet Marf and become his lifelong enemy, since the farmer is expecting to meet a great enemy and will subconsciously adjust his behavior accordingly.
So at this point, the fortune-teller is not just describing your future, they are choosing it.
When the fortune teller chooses a terrible future for you, this is a future curse, as in. . .
"Your toes will be devoured by turtles by Tuesday!" the hag screamed, "and the rest of you shall follow by Friday!"
Running away, with the stolen pig on his shoulder, Trujillo shivered. He knew it was true.
This is why you can sometimes avoid curses by ignoring witches and priests. Sticking wax in your ears helps. So does singing loud songs, in order that the curses might be drowned out. It is also why witches are rarely allowed to speak at their own trials.
So far we've only talked about prophecies that were true. But what about false prophecies?
And by false prophecies, I mean ones made by prophets who describe the future as A, thereby causing future B to come about. To outside appearances, they appear to have made a shoddy prophecy, since the prophecy did not come to pass. But the prophet knows better, because they got exactly the future that they wanted. For example. . .
A scribe walks into a fortune-tellers and asks to know his future. The fortune teller knows that if she tells him "you will die alone and unloved", the scribe will strive to win a good wife, and will eventually succeed. But the fortune teller is annoyed at the scribe, because he sat on her cat, and so she tells him "you will find wealth if you invest in your education", knowing that she has ensured that he will be eaten by crocodiles in the next three days.
This is why false prophets are often rich prophets. If you are in the business of choosing small, local futures, you have given yourself quite an advantage.
But since the words of a prophecy don't always line up with the known future of a prophecy, there are many cases where a prophet will want to deliver a false prophecy in order to bring about some other event. Do you want a true prophecy or a useful one? This is yet another reason why prophecies (seem to) fail so often.
But at the same time, some of your prophecies need to come true, otherwise no one will listen to you. And your ability to impact the future depends on your ability to influence the present.
The fisherman and the scribe might not heed the words of the fortune-teller if the fortune-teller is some dusty beggar on a street corner. But they'll have a hard time ignoring the prophecies of a jewel-clad oracle, wreathed in illegal smokes, sitting atop a drugged and bloody elephant, while her prophecies are repeated in monotone by a pair of painted ogres.
Prophecy exists at the intersection of information theory, game theory, and popular fashion.
And so a prophet's power is proportionate to how much attention that prophet gets, multiplied by their own ability to prophecy. A prophet who is weaker in prophecy might be able to overpower a stronger prophet simply by being better at getting attention.
Actually, the full formula is closer to prophetic ability X ostentatiousness X the distance to the nearest other prophet. Remember how prophecies are only valid until they collide with another prophecy? Since only the most recent prophecy is valid, and since the timeline gets muddied as events ripple out from where a prophecy is learned, it behooves a prophet
(And yes, prophets kill each other all the time. This is mostly because two prophets working in the same area will often nullify each other's prophecies. These murders are always extremely indirect things. No prophet has ever been arrested for killing another prophet, because such murders are very subtle. Additionally, such murders are usually carried out against children who will become prophets themselves some day. Prophets are great and subtle killers of children, although no one knows it.)
These are brave clerics of St. Chantissa, the patron saint of random chance. Each one carries a relic with them: a six-sided die blessed by the saintess herself. These dice are exempt from the deterministic laws that govern the universe, and these clerics use their dice to determine everything from where they will eat, to who they will marry, to what they should do today. The dice are truly random number generators.
They carry books of random actions that can be undertaken, and vast tables of proscribed actions that must be taken according to the dice.
These books are not holy, nor are they uniform, but it is important to have an order so that they can have perfect chaos.
They are in great demand as breakers of curses. Has a powerful witch declared that you will be gnawed to death by rats before the next full moon? She is probably right; you should go find a prophecy breaker immediately!
The prophecy breaker's services usually involve rushing around and doing what amounts to a random quest for the church. It might involve breaking into a house, stealing all of the hats in a house, putting the hats on sleeping horses all around town, and then slaying a local owlbear while armed with only carpenter's hammers.
Yes, this is excessive, knowing what we (the readers) do about causality.
Yes, some of the stuff the prophecy breakers do seems illegal, and possibly even immoral (even if someone is eventually compensated for their hats). But the Church tolerates them because it sometimes depends on them. (They famously saved Centerra by avoiding a comet that was heading straight for the planet. No one is quite sure how that worked, but it did.)
Prophecy breakers tend to be quirky-as-fuck individuals. For example, Flartlebee the Cat Eater has four braids of hair, each dyed a different color, with the rest of her head shaved. She drinks tea every hour on the hour from a locked stein and rides a giant bird named King Flart. She avoids saying words that begin with 'o' and avoid the floor whenever possible, preferring to walk on furniture, or be carried.
Some Prophetic Curses. [d6]
The only cures are prophecy breakers, getting your fortune told, or 2d4 weeks.
1 You will die in a fire. - The next time fire damage brings you down to 0 HP, you automatically die.
2 You will die alone. - Whenever you are alone, you take double damage.
3 Poison shall blister your veins. - Whenever poison could potentially kill you, it does.
4 You shall be devoured alive. - You fail all checks to avoid being devoured alive. If there is a monster on the wandering monster table that could potentially swallow you, you will encounter it on the first wandering monster roll.
5 You shall be devoured by someone you trust. - The first time a hireling could potentially betray you to disastrous effect, they will do so.
6 You shall die in the wilderness. - As soon as you are out in the wilderness and run into trouble (i.e. out of rations) you will get lost for 1d6 days.
Fate is something different entirely. This is when some future event is decided by the spirits (unincorporated angels and demons) and they decide that this event is going to pass no matter what.
Fate is infuriating and everyone hates it.