I'm curious to hear your reasoning for this.
Ok.
If you only have one lens, you will have to shoot images with only that one focal length in mind.
In the case of a zoom, you'll have limited focal lengths but won't have a bag full of lenses that give you many choices.
Limiting the focal lengths lessens what you can shoot.
It forces you to look only for shots that will work with the focal length you have available.
You are immediately limited as to what you can take but also more focused on what you
can take.
You are no longer considering
everything around you. Many distractions are eliminated.
You now look at less and consider more.
Let's say you went out with a 50mm lens only.
Imo, you will likely come back with better 50mm images from your 50mm than if you went out with your 50mm and all your other lenses.
Using just a single lens for a period also allows you to really start to learn the lens.
All your images will be from the same lens.
You may start to grasp and see things from that lens you never noticed before.
You never likely viewed enough images together at one time from the same lens to notice certain things.
You may start to see the lens's strengths and weaknesses or the subjects that work really well with the focal length.
Then of course there is also less weight to carry or less messing around with changing lenses.
Either or both I would say will make the photographer happier, more eager to shoot and will keep them shooting longer.