Win probability, not margin

alphago maximises its probability of winning and doesn't care whether it wins by one point or fifty. When ahead, it plays "slack moves" that look lazy to humans, giving up territory for certainty. Commentators learned to read a slow move as a tell that AlphaGo thinks it's winning.

The insight for Go players: humans had been using score margin as a proxy for safety ("the bigger my margin, the more confident I am"), but they are different objectives. "The lessons AlphaGo is teaching us are going to influence how Go is played for the next thousand years." Source: report