This is why I never felt comfortable enough to use one of those. A have a formula for generating passwords for each account so I only have to remember that instead of individual passwords. I know password manager might be more convenient but I'm too used to the way I've been doing things all these years...
What's more likely: forgetting the master password to your password manager or one of the many passwords you have memorized? I totally get not wanting to trust a hosted service with all of your passwords in case it disappears (having an offline backup would remedy that), but not using one out of fear of forgetting a master password is overblown.
You can always do the mostly sane thing of having a master password to your main vault as the only saved password of different password vault, i.e bitwardens master password saved in an encyrpted keepass file. You have 2 passwords to remember, but also a fail safe if you forget one.
That or just write it down somewhere safe and sane.
I get what you mean and you're right. It's just that I got used to how I memorize my passwords and so far haven't really felt the need to try a manager (yet).
I used to do this, there's always a slight worry that some place will get a couple of your passwords and be able to figure out your formula the chances are pretty slim. Were the real pain came from me, when a website forces you to change your password, or they require some limit to the letters numbers and punctuation that wouldn't allow me to use my formula. I had a growing list of websites that had more exceptions.
I started out using LastPass because it's what work used which was obviously a bad idea. When it came time to leave them I moved to bitwarden which has been pretty fantastic but I mainly use it because I need to share passwords amongst my family and I really like the TOTP integration.
If I didn't have that need I would probably use KeypassX and throw it's database into a Dropbox or Syncthing.