What enabling a macro does

I have a macro I wrote a while ago that enables another macro, which does its thing then disables itself. I was reviewing the first macro, and I realized I didn’t understand what made the newly enabled macro actually perform its actions. I would (currently) think that enabling a macro just made it available for execution by triggers or, following good form (see below), enabling it for invocation by other macros. However the second macro executes as soon as the first macro enables it. I don’t understand that.

The following is relevant:

Enabling a macro enables it, it does not trigger it. It might be triggered immediately if it was configured to trigger every second, or otherwise something else must trigger it.