Big blind

Three things: the larger of the two forced bets posted before the cards; the player immediately left of the small blind who posts it; and the unit everything in poker is measured in — stack sizes, bet sizes and win rates.

Because you act last before the flop but first on every street after it, and you have money in the pot with a random hand. It is the single biggest losing position in poker — good players aim to lose less from it, not to profit.

Wider than instinct suggests, because the money already posted improves your price. Against a late-position raise, solid defending ranges run to a third of all hands or more — but defending wide only pays off if you can play well out of position afterwards.