Being a piece up in and endgame does not guarantee a win. You cannot checkmate with just a Bishop and King against a King. Sometimes you can’t even win with King, Bishop and Pawn against a bare King.
In this week’s problem, White is a piece up. But he still has some work to do to win the endgame, because Black can make a draw if he can swap off the last remaining set of pawns.
How does White to play win?
The solution to last Monday’s problem is that White plays 1 f5 and Black’s position collapses. We open up the position before Black can castle, and his position falls apart.