A masochist meets a sadist. The masochist says "Please hurt me!". The sadist says "No!".
(Very old joke)
Many chessplayers are familiar with helpmate problems, where the two sides work together to bring about a mate. But another problem genre is the selfmate. In this form of problem, White moves first and tries to force Black to mate him. Black is trying NOT to mate White. It is the chessboard equivalent of the masochist coming up against the sadist.
Success in such problems usually involves White bringing about a situation where the black king is in check, and the only way out is to play a move, which itself mates the white king. The following is an example to raise a smile. It is pretty hard to imagine the scanty Black army mating the white king, which has so much freedom. However, by a careful manoeuvre, the black pieces are lured down the board, rank by rank, until eventually, he is forced to administer the coup de grace. The problem comes from the selection to be found on the BCPS website.