People use the same password everywhere and when the sys admin forces an updated they increment the number at the end or beginning by 1.
I call it password++ .
Discussion
This is why 2FA was invented. You have to break both things, but they can always be the same two things.
lol
i've had the same password since late 90s's
its 12 random letters, numbers, characters that I forced myself to remember...
Of course I only ever changed the 1st and last characters every few months.