To get around this, people resort to writing their passwords on Post-it's, storing them in a spreadsheet or using the same password for each of their accounts.
This is really insecure. Especially if you use the same password for everything. Once one of your online accounts is hacked, the hacker will have access to all of your other accounts too.
A solution to this is using a Password Manager, a program that will store all of your passwords in a secure file.
This way, you only need to remember one password to unlock the program. The password manager will remember the rest for you.