Same Weight, Different Body

Two people can weigh exactly the same and look nothing alike. Take 160 pounds at 15% body fat: lean, defined, athletic. Now take 160 pounds at 35% body fat: softer, with more health risk. The number is identical.

The scale cannot tell muscle from fat — it only sums everything up. A pound of muscle and a pound of fat weigh the same, but muscle is denser, so a pound of it takes up noticeably less room on your frame than a pound of fat.