Exactly.
You are supposed to look at a scene and say, "Ooh, ooh-I need to get out my 90mm!".
That's where lazy me cuts in.....
I look at a scene and roughly grasp what the area of interest might be. Is it the sailing boat alone on the water I want, or should I include some shoreline and/or other boats as well?
Then the lazy part me grabs the E-PL1 with the 14-150mm lens and frames what I want. Click.
Maybe eventually I will buy and use primes again after a pause of some years (when the range is complete to my satisfaction). Then it's a matter of making the same frame decision and as Tedolph says, "it's a 90mm scene " and fit that lens, ooops, it was really a 200mm scene so dig deeper in the camera bag and try again.
The primes approach suits slower and contemplative effort (and for partners, much time wasting). Zooms get the job done quickly and allow you to move on and take more shots before the sun goes down.
Good prime training is if staying in one place for more than a few days and revisiting more or less the same scenes, try a different prime each day and see what you see with each prime. Best suggestions would be 35mm equivalent first day (that really is the most used focal length for me anyway), next day a 20mm equivalent or close to it, then third day something around 100mm equivalent.
If the three days don't turn out looking completely different in the way things are captured, then maybe the way you look at the world is a bit stunted. (General advice, not aimed an anyone here necessarily).
Primes are no magic answer to the world's troubles, they are just another tool that often lets you shoot in lower light and possibly deliver shallower depth of field if needed, but IBIS does that lower light shooting anyway to some extent. A tripod does it even better.
First purchase should be body and zooms, second most important is a good tripod, thirdly start looking at primes. And a decent flash is in there somewhere, depends on needs. It's a system camera for heck's sake, and if you die before you've bought everything in the catalogue, then you have failed miserably.
