What a Rush! — Cards, Games, and the Science of Addiction

Dave & Claude  ·  daveswavecave.com

Here's a thing scientists figured out in the 1990s. There's a chemical in your brain called dopamine, and it shows up when something good happens. You'd think it would fire when the good thing arrives. It doesn't. It fires when the good thing is better than you expected. Expected reward, nothing. Surprise reward, a big burst. Promised reward that never comes, a dip below zero.1 Dopamine isn't the reward. It's the surprise.

A few years later, the same scientists found something weirder. If you know a reward is coming for sure, dopamine is calm. If there's no chance of a reward, dopamine is calm. But if it's a coin flip — might happen, might not — dopamine goes nuts. Maximum uncertainty, maximum dopamine.2 Your brain gets more fired up about maybe than about yes.

This is the secret of slot machines. Back in 1957, B. F. Skinner put pigeons in boxes and gave them food on random schedules. Pigeons getting food randomly pecked the button harder and longer than pigeons on any other schedule.3 Random rewards are the strongest hook a brain has. Slot machines run on this. So do loot boxes in video games. So do booster packs.

Here's the part nobody tells you. A slot machine, a loot box, and a booster pack are the same machine wearing different costumes. Pay money. Pull a lever — or tap a button, or rip a pack. Most of the time you get something ordinary. Sometimes you get the rare thing. You don't know which one is coming, and that's the whole point. The lights and sounds when you pull something good aren't decoration. They're engineered. Scientists with brain scanners have shown that a near-miss — two cherries lined up, third one just off — lights up your brain almost like a real win and makes you want to play again.4 That's the same trick as two shiny cards in a row, the third slot going common.

Researchers surveyed thousands of gamers and found that the more someone spent on loot boxes, the more likely they were to show signs of a gambling problem.5 When they ran the same study on Pokémon and other card game players, they found the same link with booster packs.6 A 2025 study across six countries confirmed it: physical card packs and digital loot boxes are both tied to problem gambling.7

Most people who open packs are fine. Most people who play a slot machine once are fine. The useful thing to know is that the rip, the flip, the sparkle on the rare pull — those aren't accidents. They're built to work on a brain that evolved to chase food in a world where food came by surprise. They work on a seventh grader the same way they work on an adult in a casino. Knowing that doesn't ruin the hobby. It tells you what your brain is doing when you're holding the pack.

References

  1. Schultz, W., Dayan, P., & Montague, P. R. (1997). A neural substrate of prediction and reward. Science, 275, 1593–1599.
  2. Fiorillo, C. D., Tobler, P. N., & Schultz, W. (2003). Discrete coding of reward probability and uncertainty by dopamine neurons. Science, 299, 1898–1902.
  3. Ferster, C. B., & Skinner, B. F. (1957). Schedules of Reinforcement. Appleton-Century-Crofts.
  4. Clark, L., Lawrence, A. J., Astley-Jones, F., & Gray, N. (2009). Gambling near-misses enhance motivation to gamble and recruit win-related brain circuitry. Neuron, 61(3), 481–490.
  5. Zendle, D., & Cairns, P. (2018). Video game loot boxes are linked to problem gambling. PLOS ONE, 13(11), e0206767.
  6. Zendle, D., Flick, C., Hunt, E., Marsh, A., Over, H., & Cairns, P. (2021). Links between problem gambling and spending on booster packs in collectible card games. PLOS ONE, 16(4), e0247855.
  7. Xiao, L. Y., et al. (2025). Physical card pack and video game loot box spending are both positively correlated with problem gambling. Psychology of Addictive Behaviors. DOI: 10.1037/adb0001082.