Maybe it was already discussed. After browsing through some alike questions here about password management, I still would like to ask this question.
If there are 100 sites which require username password to login. It would be a nightmare to make up another username and password just for the uniqueness. However if we use the same username and password, we expose ourselves to crossite attack. Maybe we can make 100 different username and password, but how can we remember it?
Brain is not trustworthy. Professionals recommend not to write down any password on paper. And there are those password management software. I've never used these software so I am rather blind there. Do you trust those things? Imagine if someone stole your computer and try to break into these software, do you has the risk to lose all your identity?