More on gambler’s ruin

The original meaning is that a gambler who raises his bet to a fixed fraction of bankroll when he wins, but does not reduce it when he loses, will eventually go broke, even if he has a positive expected value on each bet.
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Consider a gambler who raises his stake to Bankroll / N when he wins, but does not reduce his stake when he loses. This general pattern is not uncommon among real gamblers, and casinos encourage it by “chipping up” winners. If he loses N bets in a row at any time, he will go broke. He will eventually lose N bets in a row, however big N is.
- Wikipedia

I have a suspicion most of the decent players in poker go busto because of this.

Fixed fractional position sizing is frequently recommended in trading, with 50 for N. (“don’t risk more than 2% of your bankroll on any one trade”)

For more on choosing N, see Kelly Criterion. Sometimes called optimal-f in trader speak.