If I use my same password on every site I visit, if ANY of those sites is compromised, now all sites are compromised. Thus, the surface area to attack is MUCH larger. Yes, one problem is that if one password gets figured out, then it gives much more access as a single point of failure, but the bigger problem is that the same password is stored in many different places.

There are two primary problems with sharing passwords for multiple accounts. Password renewal is like protesting against the ambient wetness while on board the Titanic. Also, the possibility of an attacker stealing your master password is already serious enough: if the attacker got to that point, you are already in deep trouble. Changing your master password may 'kick out' attackers would could steal your master password, but this would not change the site-specific passwords stored in the password manager, so the attacker is not totally evicted. Password renewal is a controversial issue. The usual rules for password hygiene still apply: generate your password(s) with randomness, not wit don't type a password on a machine which could be infected with a key logger beware of shoulder surfers. 15 random letters and digits ought to be enough to thwart CPU-based attackers: if your password gets stolen, it will not be through a brute force attack. To live with that, make your master password strong enough to deter attacks. This is unavoidable: I am just stating the obvious, twice, with two slightly distinct points of view. But this means that knowing that one password is sufficient to gain access to all the stored passwords. With a password manager, it suffices to remember one password to gain access to all the others. A password manager is a tool to 'remember' more passwords than what the human mind can cope with. This concentration of password power is consubstantial with the concept of a password manager.

One password vs lastpass