Exactly. There was that betting thing he did a few months back. Basically if the odds on a horse winning a race are 6-1 then if six people all put money on different horses, one is likely to win. Then he magnified that over several races, and told people he had a 'system'. One woman won money on six out of six of her races, and assumed that Derren's system was foolproof. Of course all he had done was involve about 3000 people - the probability of one of them winning money on all six races was 1.0 - he'd fixed it. But the one person on the ground who won all the races (and obviously didn't know about the 2999 other people) thought it was amazing, and bet her life savings on the next race, and lost
A lot of the stuff he does is likely - it might only work 1 in 10 times or less. But of course you don't see the failed attempts, and when it does work, it looks amazing.