One of my banks has "eight digit, numbers only, cannot repeat numbers", and each time I change it, it no digits must me replaced in the same place as the last password. No three digits must be consecutive numbers, or consecutive in reverse order. Amongst other conditions.
Generating a rememerable password is extremely hard. Even random numbers are of little use, since they tend to be rejected as well.
This results in me having to use keepassx (instead of MY BRAIN) to store my passwords.
Meanwhile, I can easily remember passwords for sites with free-form strings as password. I can even use unique ones everywhere. It would also take several centuries to brute force any of those.