Password Manager vs. Memorized Password Patterns
A memorized pattern (like a base word with predictable substitutions and a site-specific suffix) is inherently guessable once an attacker recognizes the pattern from one exposed password, while a password manager generates and stores a genuinely random, unique password per site — meaningfully more secure, at the cost of dependency on the manager itself being secured properly.
Memorized password patterns feel secure because they're personal and non-obvious to a casual observer, but they fail against exactly the kind of systematic analysis a real breach exposes them to.
Why a personal pattern is weaker than it feels
A pattern like "Basewordsitename!23" feels unique to the person using it, but if any single password following that pattern is exposed in a breach, the underlying structure becomes visible — an attacker (or automated tool) can often derive the pattern and apply it to guess passwords on other sites the same person uses, even without ever seeing those other passwords directly.
What a password manager does differently
A password manager generates a fully random, independent password for every single site, with no shared structure between them — a breach exposing one password reveals nothing usable about any other account, since there's no pattern to extrapolate from. The trade-off is that remembering dozens of random passwords isn't realistic without a tool, which is exactly the problem a password manager is built to solve.
The one password that still needs to be memorable
The password manager's own master password is the exception — it genuinely needs to be memorized (or, better, protected by a passphrase and a strong second factor), since it's the single point that unlocks everything else. This is the one place where a long, memorable passphrase is a reasonable, appropriate choice rather than a security compromise.