A company that handles Internet Security tracks the worst (i.e., easiest to guess) passwords of the year. As I think I may have mentioned, when I operated a primitive by-modem computer bulletin board back in the Antediluvian Era, a pretty large percentage of our users selected "dragon" as their password.
And some folks just picked obvious ones. A number of my users were comic book writers who used the name of their most famous character or assignment. Penn Jillette logged onto my system once and his password was the same as the name of his Showtime series. Bet he doesn't use that one anymore but a lot of other people do.
If you want an impossible-to-guess (and remember) password, go to this page and just copy some string of letters, numbers and symbols.