I dont know why you do ask this basic thing even just on our common sense we would able to know the answer and even yourself you can already pinpoint on what are the things you gonna do.

Memorizing keys literally is hard yet a string of letter and numbers cant really be easily remembered by each individual which it would have the tendency to forget and lose the access of that wallet thats why its common to write up those codes either on a paper or store it up on a notepad then keep them safe.

We do really need to remember our keys because once its lost then recovering would really be impossible.