The principle of one diagonal
Pure opposite colored bishop endings have a very large drawish tendency. If the defender is dug in on squares of his own bishop his fortress usually cannot be stormed. But no rule without exceptions: why did Negi resign without waiting for Black's answer?
Note that in the replay windows below you can click on the notation to follow the game.
To exchange or not to exchange, that's the question
Before trading down into a pawn ending, you should calculate it to the end: