you are right Paul

but not only we must made a blunder,the opponent must be able to see the blunder,and take advantage of it

i can tell you that i made a blunder (well,not really a blunder,just a slightly weak move) playing a endgame in a correspondence game at LSS (the endgame that i sent you a fen position).the endgame continue to be a win for white,but with a very hard work for white,but my opponent,never saw my 'blunder' (it was a very very deep blunder),so i can transpose again to the same position,and play the good move,going into a better endgame,exchanging one of the rooks,and going into an easy win endgame

Paul,you sent me a link to the same page were we are?