Base password plus company name or initials. One password mutated into infinite variations that are easy to remember. This has been working fine for me for at least 15 years.
So if someone finds out your password for a certain site is `Facebook1234ABCD` they have a fair guess at every other password?
Same applies for `MyPasswordFB` using the reverse method.
So in the end the password contains numbers, letters both capped and lower case and special characters.
You just need one little website to leak passwords in plaintext and all your passwords are up for grabs.
I used to do the same thing and I stopped for that reason.