Here is rook and pawn ending of a type that occurs frequently in blitz chess. With both sides about to promote a pawn, the general result is a draw. One side will give up his rook for the opponent's pawn, and will then force his opponent to do the same.
I am White in the diagram position and my last move was 57.g7. Black has several ways to force a draw, the simplest of which is 57...Rh4+ 58. Kg8 b2 59.Rb8 Rb4 60.Rxb4 Kxb4 61.Kf8 b1Q g8Q and there is no play left for either side.
However, my opponent apparently believed there was absolutely no danger and that he could play anything he liked. That's how he came up with:
A golden opportunity for White!
Black is now on the horns of a dilemma. If 3...Kb4 then 4.Qb8+ picks up the rook with an easy win. The same goes for 3...Kc3 4.Qg3+. All other moves (except 3...Rf7) allow 4.Qxb3, and White reaches the winning ending of queen vs rook. There was nothing left for Black but resignation.
The lesson here is that no matter how harmless a position may appear, it is still possible to fall into a trap!