Swimmers learn exactly how long they can go before they need air. Learn your own limit before you’re gasping.

Capacity is knowable in advance, but almost nobody measures it until they have blown past it. A swimmer counts strokes and learns the number cold, so the decision about air gets made before panic has a vote. The same applies to how many late nights, shifts or commitments you can stack before you come apart.

Find your number by noticing where the fraying starts. Three late nights, two doubles in a row, a week with no time alone. Then build the breath in before that point, since a planned rest costs far less than a collapse.