Know what you’re like on four hours of sleep, so you don’t mistake exhaustion for your real personality.

Tiredness produces a convincing impersonation of a personality. Short temper, no interest in anything, a bleak reading of your prospects: all of it feels like the truth finally showing through, when it is closer to a temporary state with an explanation. The mistake is taking the readings from the worst hardware conditions as the accurate ones.

Learn what you specifically become when you are short on sleep, and write it down while you are rested. Then recognise it when it happens. Decide nothing important in that state, and revisit any conclusion you reached there once you have slept.