But although we have known for years that human memory works best when the information is linked and meaningful in some way, we try to remember meaningless passwords because they are ``more secure."
On top of this, there are simply so many passwords to remember. Clear makes a long list of the security mechanisms and their related keys, cards, userIDs, PINs, user names, passwords, etc. that are required by a single university educator [Clear, 2002]. While each individual system may seem reasonable, the whole amounts to a huge mental load, especially when some of the passwords and PINs are not used frequently. For many people, the load becomes too great and they must rely on external reminders (sticky notes, palm pilots, etc.) to cope.
These two issues related to memory (difficulty of remembering non-meaningful items and number of items that must be remembered) are probably the most significant, but they are not the only issues related to human memory that need to be considered. Sasse et al. list the most important memory issues as follows [Sasse et al., 2001]: