Not single sign on = infinite points of failure

This is mathematically misleading. SSO adds a single global point of failure on top of the existing system. Single nodes will still fail in both circumstances, unaffected by the use or not of SSO.

I am not just talking about node failures but about the human failure too. The human cannot manage and remember accounts for a hundred services.

LastPass can for people, and automation can for machines. And then you are the one point of control of your destiny, not the SSO namespace owner.

And that makes LastPass your SSO :p

There still are infinite points of failure with SSO. Each service would need a trust relationship established with the SSO provider, any of which is a point of failure.