Am 29.05.21 um 09:11 schrieb Felipe Contreras:

Now that the code has been simplified and it's clear what it's
actually doing, update the documentation to reflect that.

Namely; the simple mode only barfs when working on a centralized
workflow, and there's no configured upstream branch with the same name.

[...]

+* `simple` - pushes the current branch with the same name on the remote.
+If you are working on a centralized workflow (pushing to the same repository you
+pull from, which is typically `origin`), then you need to configure an upstream
+branch with the same name.

I'd like to remark that I personally find the following description of 
`push.default=simple`, taken from the git push man page [1], easier to 
understand:

The current branch is pushed to the corresponding upstream branch, but
as a safety measure, the push is aborted if the upstream branch does not
have the same name as the local one.

[1] https://git-scm.com/docs/git-push#_description