Steven Poole in The Guardian:
The outguessing machines played a very simple game. Every round, both machine and human player pick one of two choices: heads or tails, left or right. It is decided beforehand that if the choices match, one player scores a point, whereas if they are different, the other player scores. What happens is that, over dozens of rounds, humans fall into unconscious patterns that a computer can recognise, and therefore anticipate. In this way, with only 16 bits of memory (16 ones or zeroes), a machine by the information theorist Claude Shannon was able to beat all comers. To call this “outsmarting” the humans is perhaps a bit of a stretch, but it is what Poundstone means by the term when he goes on to apply it to different areas. Indeed there are a surprising number of areas where a similar kind of “outguessing” strategy can be fruitful. Rock, Paper, Scissors is a random game, but because most people deviate from true randomness, it is possible to have a strategy. (“A player who loses is more likely to switch to a different throw the next time,” Poundstone explains as an example.) In tennis, too, most players alternate their directions of serve too regularly, so Poundstone recommends using a wristwatch or heart-rate monitor to properly randomise them.
More here.