Mistake - whose stake is it anyway ?

There are so many times we volunteer to point out a mistake of someone's of course! And this seems so easy to pass the buck/blame, though it feels like doomsday when you are at the receiving end.

If a person 'A' blames another person 'B', does it make 'A' a hero ?
Hmm.. Listening to A's, 'I told you then,... ' or 'I wish you had done this way .... ' or 'You should have asked my help .. ' is probably one of the most nauseating experiences for 'B'.

I think if B commits an error/mistake 'E' and 'A' is able to point the mistake 'E', then 'A' by default becomes a stake-holder in this mistake 'E'. Thus, the moment 'A' identifies the problem he is also part and parcel of the problem and there is no way 'A' can play the holy ghost by lecturing that 'this could have been done that way'.