Memorizing gets you one answer. Understanding gets you the next ten.

Memorized facts sit in place and do nothing when the question gets reworded. Understanding is knowing why the fact is the way it is, which means you can rebuild it, notice when it does not apply, and use it on something you have never seen. The first takes less effort now and keeps charging you. The second is harder up front and then starts paying.

After you learn something, check which one you have. Try explaining why it works, or try a version of the question with the numbers changed. If it collapses, you memorized it, and now you know exactly where to go back to.