The difficulty of computer Go is being built up and overstated, largely by tech media in search of a "next big thing" along the lines of Deep Blue or Watson. Expect a lot of hype around this in the coming months, but a predictable conclusion. Why would Google put it's reputation on the line for something like this if it wasn't really sure that it was going to win? The same question could have been asked about Watson or Deep Blue in their competitions. Google has no external deadline pressure to do this publicity stunt, meaning that they were able to wait until they were near certain of victory. Sedol probably doesn't mind that the odds are stacked against him because the match will raise his public profile either way.

Go is hard, but I can't see why Google would do this unless they think they have a big advantage.

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Drew
made a comment:

Makes sense, but if you look at the history of Man v. Machine contests, e.g. chess or poker, in the beginning, sponsors of the Machine were willing to take a loss for publicity and to get a chance to learn. It's only a few years after the first match that they finally got the win.

https://en.wikipedia.org/wiki/Human%E2%80%93computer_chess_matches (serious effort involving big corps starting late 80s)

https://en.wikipedia.org/wiki/Computer_poker_players (serious effort starting I'd say at 2005).

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