[twblalock]

This also happens in the sports betting world. People use this method to convince others that they can consistently predict the outcome of games, or the spread, or the other stuff people want to bet on.

[coriny]

Nicely demonstrated in Derren Brown's "The System": https://www.youtube.com/watch?v=9R5OWh7luL4.

Though we've rather ruined the twist ...