Rest and Recovery (Principles of Weight Training) | Fitness and Exercise Glossary
Rest and recovery is the fourth principle of weight training. It says that each muscle requires adequate time to rest and recover between workouts.
The actual duration of the rest and recovery period may vary from individual-to-individual based on factors like their current physical condition, prior weight training experience, diet, and the intensity and volume of their training.
A good rule of thumb is to provide 48 hours of rest and recovery time before working the same muscle again.
Also see: principles of weight training
Category: Fitness, Health & Exercise Glossary

I definitely agree with this one. This should serve as a reminder for everyone who works out. Muscles need to rest. Some people overexercise and put too much stress on the muscles which can be bad.