If you take an intense color and put an intense complement next to it without graying it, it's very hot. The gray allows the eye to do the visual mixing.
When I rest, I rest and when I work, I work hard and sometimes for long hours. I always try to be rested when I work.
Laying complements next to each other makes them scintillating, but mixing them produces a 'muddy' rendering of each color. The mud is good stuff.