An unfinished exercise can show exactly where your understanding stopped being clear.

Where you stopped is the most useful information in the whole attempt. It marks the precise line between what you understood and what you only recognized, and that line is invisible once somebody hands you the finished answer. An abandoned exercise is not wasted effort. It is a map with a pin in the exact place worth working on.

Stop when you get stuck and write down what you could not decide. Leave it there rather than reaching for the solution. Come back with that note and work only on the gap it names, which is usually smaller than the sense of being lost suggested.