Right now I don't know if I'm more impressed by AlphaGo's artificial intelligence or its artificial stupidity.
Lee Sedol won because he played extremely well. But when AlphaGo was already losing it made some very bad moves. One of them was so bad that it's the kind of mistake you would only expect from someone who's starting to learn how to play Go.
AlphaGo kept making bad moves in such a way the rest of the game becomes more and more predictable - each of the moves Lee Sedol makes could be described as the only obvious one.
On the surface, as an analogy, it sounds like investors in financial markets, capitulating, selling at a loss for a more risky outcome. In hindsight almost always bad moves, but at the time of making them it feels right because it's removing risk. Investors are losing, and then when capitulating they make even worse moves, like selling at market bottoms.
Lee Sedol won because he played extremely well. But when AlphaGo was already losing it made some very bad moves. One of them was so bad that it's the kind of mistake you would only expect from someone who's starting to learn how to play Go.