My wife is a design geek who uses iPhone and SkechUp 3D software. Yet does not remember almost no passwords and phone numbers. I admit I cannot reproduce any mobile number of my contacts either without checking my phone, even my own number. Imagine she travels far and her iPhone gets lost, then what? Who would she get in touch with? Phone directory? Those paper monster books, do they still exist? These days it is easy to be vulnerable without paper records and good memory, yet it contradicts our technology-advanced present. My kid was playing once with my iPhone which has company-set protection for pin guessing. After the sixth try — poof! — the phone erased itself, making the phone as useful as a brick.
Anyway, what I started doing some time ago, I print essential information like phone numbers and keep those memos in a safe place. To write in stone would be better, but they are too heavy to travel with.