Sleep isn’t the opposite of working hard. It’s the part where your brain saves the file.

Learning does not finish when you close the book. Most of the consolidating happens while you are asleep, so cutting sleep to study longer removes the step that turns effort into memory. You end up with more hours logged and less of it retained, and then assume the material was unusually hard. It was hard, and so was the schedule you gave yourself.

When the choice late at night is another hour of revision or an hour of sleep, take the sleep more often than feels responsible. Start earlier instead. Work only counts if it stays.