Ergodicity is illustrated by Russian roulette: six people each playing once with a billion-dollar prize leaves five billionaires and one dead, but one person playing six times with the same gun ends up worth zero — demonstrating that what is true for many people on average is not the same as one person repeating the gamble.

The Kelly criterion is a mathematical formulation of the simple concept 'don't risk everything' — bet carefully each time so you never lose the whole kitty — and it helps avoid ruin, making risk-taking calculated across large populations not always rational for an individual.

The number one way people get ruined in modern business is not betting too much but cutting corners and doing unethical or illegal things; ending up in prison or with a ruined reputation is equivalent to being wiped to zero, so reputational ruin should be treated as ergodic ruin and avoided absolutely.