Losing hurts twice as much

Psychologists Daniel Kahneman and Amos Tversky measured it in the nineteen-seventies: losing 100 € hurts, on average, about twice as much as gaining 100 € feels good. They called it loss aversion, and it's probably the bias that costs the most money.

Its symptoms are easy to recognize. Selling in a panic when the market falls, turning a temporary loss into a permanent one. Clinging to a bad investment "until I get my money back." Or the costliest of all: never investing so as never to lose, while inflation quietly discounts value year after year without asking permission.

You can't uninstall the bias, but you can design around it: automate your contributions, look at your portfolio just a few times a year, and set your rules before the storm, not during it. Against an ancient brain, modern procedures.