When I was a SysAdmin, people used to be AMAZED at how easily I could get into almost any password-protected computer. They would ask me for my tips and tricks and techniques, what software I used, how I would get around multiple password attempt blockers, etc.
Like a magician, I would never reveal my secrets.
However, the truth is that I worked for a government agency that required monthly password changes. Nobody could keep up with that pace of unique password-generation requirements, so everyone kept a note somewhere...
Or used their wife's name. Or their license plate number. Or their wedding date. Or baby's birthday.
Normally it was just written on a Post-It somewhere around the desk, under the keyboard, in a drawer, or ... like in this photo ... simply stuck to the front of the monitor.