1. Use the same password for all logins because you don't know how to manage unique passwords for all your logins. Obviously this is about as unsecure as you can get.
2. Write your unique passwords down somewhere. This can be in a notebook, or a password manager (1password and the like). In this case, there is still a single point of failure (as you pointed out) if someone finds your book or compromises your password manager.
3. Use some sort of SSO service. Still a single point of failure (Apple, Google, Facebook).
I feel like using Apple SSO with 2-factor authentication is just as secure as any of these options.
Is there any "secure" system that doesn't have a single point of failure?