Favorite theories proved wrong

[Eddie]

No: HPFGUIDX 171986

As entertainment for the final days before DH, and for the lonely cold
days that will follow, here's a new thread:

What theories have you held -- and you were SURE you were right -- but
have since been proved wrong?

Eddie, who used to believe for certain that Dumbledore was Ron gone
back in time, but JKR says it ain't so (although I can't find the
exact quote right now)