Why does git reject two pushes in a row?

Question

Sometimes when I push changes and then push more changes I see a "rejected, not fast forward" error. I am the only one using the repository so no one else has pushed anything.

It seems to happen when I push several changes quickly, which makes me wonder if it is timing related. Sometimes I push a change and quickly push an amended correction and then I see this problem. It happens infrequently, so I have not been able to observe a repeatable pattern.

I am just confused how git could think the remote has diverged when I am the only one pushing to it? Can anyone clarify the likely causes of this issue?

Thanks