When the scale drops, you're losing some mix of fat, muscle, and water. What you want to lose is fat, while holding onto (or even building) muscle — because muscle is what gives your body the shape most people are actually chasing when they say they want to "tone up" or "lean out."

The number on the scale carries enormous emotional weight, but it's a surprisingly poor report card. It gives you a single figure — total body mass — and tells you nothing about what that mass is made of, whether you're healthier, or how you actually look. Two people can weigh exactly the same and look and feel completely different, because weight and composition are not the same thing.