For myself this kind of comfort comes of years of years of sign painting. Every day I painted something new but used exactly the same process each time so in a way it was the same thing. This made the technical part of the job completely predictable. I knew what would happen if I mix those two colors or put this warm color next to that blue or used a ragged brush stroke which lets the underpainting show through. So I could have a new idea and just paint it on the fly without fear that it wouldn't work. It will always work. It may not be great, but to some extent it will work.
Knowing those technical things is the key to creativity. Some art students and even teachers fear that if you learn too much about technique it will inhibit your creative expression. This is total nonsense. It's like saying knowing how to talk inhibits your ability to express yourself. It's literally the opposite of the truth.
Once you have an artistic vocabulary down you are free to roll with your ideas as soon as they occur to you without having to figure out how to do it. You already know how to do it so it just flows from you.
So I always knew this painting was going to work even if I tried something weird and didn't really like it, it still works on some level.
especially from a distance. I'll have to do something about that.