The one where Commander Data tries to play a grandmaster at some invented competitive logic game. Of course, everyone has very high hopes because he's essentially a computer. But he gets soundly trounced in the first game.

OF course, this being TV, he eventually has an epiphany and his second game at the end of the episode results in the grandmaster abandoning the match!

Data's epiphany? He had been playing to win, which the grandmaster knew extremely well how to counter and defeat. He changed tactics: second time he played to make the board even. The grandmaster didn't know how to counter that!

Wade.