[AnIdiotOnTheNet]

> When alphago was losing in the fourth match against Lee Sedol it would play 'stupid' moves. These were, for instance, trivial threads that any somewhat accomplished amateur go player would recognize in an instant and answer correctly.

I think this behavior is less 'stupid' than it appears. When human beings play Go, the points matter even to the loser, and everyone goes home when it is over. There is life outside of Go. To Alpha Go, Go is it's entire universe. Part of the way it was trained was competing against other instances of itself, a sort of Thunderdome where the loser doesn't get to continue existing, and doesn't contribute to future generations. To Alpha Go, defeat is death. The behavior we observe when losing is nigh-certain has a human equivalent, we call it desperation. Alpha Go is trying moves that can only possibly work if the opponent makes a catastrophic blunder, which is incredibly unlikely, but it's the only shot it has.