Why is everyone so convinced the prophecy is correct?

[tobyreiner]

No: HPFGUIDX 82188

Ok, this is *really* bugging me about both my favourite fantasy 
series now. What makes it worse is that in both cases the prophecy is 
identical and a needless, in fact, stupid, addition to the series. 

I just don't understand why Dumbledore and Voldemort are so convinced 
that Trewlawny's prophecy is correct. Is there any proof that it will 
be? Isn't it possible that her seeing eye got things out of whack? Do 
we know for certain that seers never make mistakes? 

And I don't see why readers aren't suspecting that JKR might play on 
this too. Maybe it will turn out that the prophecy is wrong. Maybe 
Harry won't be the one to vanquish Voldy. 

(While I'm at it, if any Star Wars fans out there could tell me why 
the Jedi are now so convinced that Anakin Skywalker is the "one to 
bring balance to the Force", I'd be mighty obliged. Or even that 
there is going to be any one to bring balance. We, as the audience, 
do know that there is going to be this one and that it is, indeed, 
going to be Anakin Skywalker, but the protagonists know no such 
thing).