If you log into multiple systems you should use different passwords for each. At White Sands Missile Range, we prided ourselves on our password security. However, we had a user who used the same password on our computer and another owned by a contractor. Security used that loophole to break into our system. We banished that user from our system.
People save their passwords in unusual places.
We have found them in the flip-up desk phone directories under P for password. I think the most unusual place was on the ceiling above the user's desk. He would simply lean back and read it when logging onto the computer. One of the most important duties of a system's administrator is maintaining system security. This involves both passwords and computer viruses.