Have you ever seen an expansion joint?
You see them in driveways, sidewalks, stucco walls, bridges, skyscrapers.
Stress will cause cracks, now the cracks usually aren't an immediate problem, they can be unsightly, but over time, the cracks allow moisture in, in the colder climates that can be a real issue. So the idea of expansion joints is to control the stress, create natural breaking points to prevent actual cracking.
They come from natural day to day things, activities, weather, aging.
Bill Phillips in his book body for life has a similar system. His idea is you eat right and exercise properly six days a week and take a day off. He knows that if your program is a seven days a week, eventually you'll crack, that can really mess with your psyche. So he puts expansion joints in his program.
Even in the Bible created a day off, a day of rest. Mark 2:27 The Sabbath was made for man, not man for the Sabbath.
Do you answer your phone 7 days a week? Do you take a day off?
Do you have expansion joints in your life?