The blinds are forced money. When it folds to a late-position raiser trying to steal them — a wide open made largely to win the blinds uncontested — the big blind isn't investing fresh chips; it's deciding whether to defend chips it already posted. That posted blind is a discount no other seat gets, which is why blind-defense ranges are the widest calling ranges in preflop poker.

You defend two ways: call to see a flop with a wide, capped range, or 3-bet to seize the initiative and deny the raiser a cheap look. How much you defend scales with how wide the opener's range is. Against the button — the widest steal, facing the fewest players left behind it — you defend enormously; against an under-the-gun open, a range packed with real strength, you defend far less. This app's charts show exactly that gap: the big blind defends 41% of hands versus a button open (vsrfi:BB:vs:BTN) but only 16% versus UTG (vsrfi:BB:vs:UTG) — read live, combo-weighted, from the two nodes.

The price is what makes those wide ranges profitable. Against a 2bb button open with standard 0.5/1 blinds, the pot already holds about 3.5bb and it costs you just 1.0bb more to call — roughly 3.5:1, so you only need about 22% equity to break even. A huge slice of hands clears that bar against the button's wide stealing range, which is why folding the big blind too often is one of the most common — and most expensive — leaks in the game.

Price isn't the whole story. You play every one of these pots out of position, so you convert less of your raw equity to chips than the odds suggest (the Equity realization topic makes this precise). That poor realization is the counterweight to the discount: it's why marginal hands that could flat in position are often better as a 3-bet-or-fold here, and why the big blind still folds its worst hands even at 3.5:1.