What caffeine actually does

Caffeine doesn't create energy. It blocks the signal that tells you you're tired, which makes you feel more alert for a few hours. That's genuinely useful, but it's borrowing, not generating.

The catch

When it wears off, the tiredness it was masking is still there, sometimes with interest. Late-day caffeine can also quietly erode the sleep that would have fixed the tiredness in the first place.

Using it well

Most people do best keeping caffeine earlier in the day, pairing it with water, and not relying on it to paper over a run of short nights. Think of it as one tool alongside food, movement and rest, not the whole strategy.