Where do we start? What's the first symptom? How do we know that we are looking at a new scenario?
Patterns. Patterns give us the context for word choice. They give us the right to call something 'the first'.
The 'first' is really only named 'the first' after the scenario in question happens again or runs most of--if not all of--its course.
First course. First base. First inning. Those names all work because the second (or more) exists.
Speaking of 'first courses', soup is typically a first course until soup and half sandwich is offered. Soup then becomes a different sort of 'first'. It's the first part of the meal but no longer called the first course.
Similarly, your first time in Africa is only the first time if you never go back. It's commonly referred to as your 'only time' if it's not part of a reoccurring situation.
I'm procrastinating and it's not the first time, or the only time, but it is the first thing in my writing pattern.
I write freely or I clean my desk. Only after I've done one of those habitual firsts can I focus on my work. I'm not sure why, but I stopped fighting it a few years ago.
Writing freely, like this, gives me the feeling of finishing something, and frees my mind to start something new and usually bigger.
Cleaning off my desk, and filing books on my shelf gives me the same feeling.
It makes me wonder if other people have "The first thing that I do . . . " moments that they didn't realize they did until reading this . . .