should i copy the ID & PW on a paper?
If you mean logins and password for various websites it depends. There is several tactics for that.
Some use password managers, you encrypt all other passwords and logins with one password so they can be even random, you need to remember only one.
Some use different passwords for important websites, and some one general password for less important websites. You minimize things to remember here.
Writing login/pass on paper also could work, thats why paper wallet was created for bitcoin, but it demand physical security then.