Sometimes, even having an extra bishop and pawn is not enough to win in an endgame. This occurs when the pawn is a rook pawn (meaning it is on either the a or h file), and the bishop is not on the same color as the square on which that pawn would promote.
The diagram above illustrates this type of endgame. White's pawn on a7 would like to promote to a queen on a8, a light square. Unfortunately, White only controls a dark-squared bishop, making it impossible for the bishop to help protect a8, or drive the Black king away from there. Even though it is White's move, there is no way to make progress; either White may move his king away and allow Black to shuffle his king between a8 and b7, or White can play a bishop move and stalemate Black's king.
