Common Principle: Fallow Fields, Rest Days, Buffer Weeks

Case 1: A farmer deliberately leaves a field that's been farmed for years fallow for one year. Land that never rests yields less and less. Case 2: A capable trainer designs rest days into the workout program from the start. Muscles grow not during exercise but during rest. Case 3: An experienced dev team puts a buffer week between sprints where no features are built. A team that runs nonstop will inevitably slow down months later.

Write one principle that runs through all three cases in a single sentence. Neither a sentence that fits only one case, nor a blunt sentence like 'rest is good.'