Well - if I was wrong ITFP.
I mean, you haven't been "proven wrong" if player X (say Symonds) goes from being totally rubbish to being very, very good indeed and all you were saying is "he's crap" when he was crap.
You've been proven wrong if you said "he'll never be any good", yes - but I'm pretty careful that I don't often say that, because you can never tell what's going to happen, and Symonds is one of the best examples of that - who on Earth would have predicted the course his career was going to take just before WC2003? Not many, I'd think.
If I have been proven wrong in my assessment of a player\situation\whatever, yes, I do admit it. Personally I didn't really think Flintoff would amount to much as a Test-batsman in July 2003 - but we soon found otherwise. And I did say, once or twice, "he'll never be any good". Perhaps I shouldn't have.
I do learn fast, and I can't remember the last time I said "he'll never be any good" about anyone.