The human brain can only keep track of 7 things, plus or minus 2.
Oh, how true. (Digits of pi, 41 in my case, don't count. That was just a bored day in high school physics.) Which is why I must admit to the masses that I have begun to write down some hints to the passwords required on work systems. This was a big source of frustration for me at work last Friday.
In any working environment, you're going to have a few different systems that you interact with. For me, as a contractor, it's a lot: there's this client's system; there's that client's system; there's the "mother ship" encryption scheme ... I counted, and I interact with no fewer than 7 different systems on a daily basis.
Each requires its own password. Some can have no greater than 8 characters. Some can have no fewer than 9 characters. They all must be changed quarterly, biannually, or annually.
I have no hope of keeping them straight; the Law of Requisite Parsimony is hopelessly broken. In each system's attempt to be as secure as possible, they have put me in the untenable position of keeping each system's requirements' separate and up to date. The best I can do is write reminders to myself -- hints and suggestions, not the actual passwords -- but I can't wait for the day of biometric scanners becoming more ubiquitous.