Insurance

You're all-in as a big favourite and somebody — often the underdog, sometimes a third party — offers insurance: pay a premium now, and if the bad runout arrives, you get your money back anyway. It's an actual insurance contract priced on your chance of losing, negotiated at the table while the dealer waits.

The fair price is easy to compute. You're an 80% favourite in a $500 pot. You lose one time in five, so fair insurance costs 20% of the pot — $100 — to guarantee the full $500 back on a loss. Pay $100 and your outcome locks at +$400 regardless of the river. Pay anything more and you're donating EV; pay less and the insurer is. In practice, whoever offers insurance prices it worse than fair, because that's why they're offering.

Compare running it twice, which buys the same peace of mind for free: variance drops, EV untouched. Insurance is only worth considering when running it twice isn't on the table and the pot is large enough relative to your bankroll that the premium is a reasonable fee for survival. For ordinary pots, insuring is a leak dressed up as prudence.

At home games, insurance deals get invented mid-hand with creative arithmetic. If you take them at all, take them at fair odds or better, and make sure the seller can actually pay — an insurance policy from a broke opponent is a marker in a cheap suit. The house rules conversation should cover whether side deals like this are allowed at all. The simplest house rule is also the most common one: no side deals at the table, run it twice if both players agree, and let the cards decide the rest.