In this era of information technology everyone is bombarded with tons of data that they don't know how to think and memorize
Thinking and memorizing can strengthen your brain muscles but people hate exercising their bodies and their brains
I do use keepass for managing different passwords, but I kind of memorize most of them, only open keepass for storing them in case I ever forget
I can memorise af58f916cc0cb22193c18f02d3c1cc3e easily, but once you work out (perhaps a keylogger) why that's my paypal password, my google password of 68b31385067f73977c6007cefcddbe74 falls quickly
Back in 2012, my facebook password was idontunderstandthepointofonlinefriends2011. I don't think it's easy to forget something like that.
Easy to remember, and you'd have to be very determined to get the link between them even if both were compromised, but if the plain text version was compromised then it would compromise the entire system
That's the most secure system I can think of which doesn't involve remembering thousands of complex random passwords. Sure I can remember "correcthorsebatterystaple", but can I remember which 4 words for which specific site?
I'll admit I'm probably an exceptional case but regular users must have 100 or more password after a couple of years online.