Jonah Lehrer pegs slot machine addiction to the brain's love of pattern recognition:

[It] helps to think about the slot machine from the perspective of your dopamine neurons. While you are losing money, your neurons are struggling to decipher the patterns inside the machine. They want to understand the game, to decode the logic of luck, to find the events that predict a payout.

But here's the catch: slot machines can't be solved. They use random number generators to determine their payout. There are no patterns or algorithms to uncover; studying our near-misses won't tell us how to win. There is only a stupid little microchip, churning out arbitrary digits. At this point, our dopamine neurons should just surrender: the slot machine is a waste of mental energy. But this isn't what happens. Instead of getting bored by the haphazard payouts, our dopamine neurons become obsessed. When we pull the lever and get a lucky reward, we experience a rush of pleasurable dopamine precisely because the reward was so unexpected.

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