The first condition of education is being able to put someone to wholesome and meaningful work.

Learning attaches itself to a task. Instruction with nothing to apply it to slides off, while the same material handed to somebody who needs it for a real job sticks almost without effort. The condition being named is not discipline but purpose, which is why so much teaching fails on people who cannot see what it is for.

If something will not stay in your head, give it a job. Find a small real use for what you are learning this week, however trivial, and let the use pull the knowledge in. The same trick works on anyone you are trying to teach, and it works better than repetition.