The "inner core" of the tape measure has a small piece of steel in it, which acts like a spring. You can also think of it this way, it is the one on the trigger of the toy pistol, the small wire used to "strike" the bullet, when it is pulled out, it will be bent by force, and the external force after release (refers to the force of hand pulling, while the friction force is stronger than the friction force). Small, less than the elasticity of the small wire) disappears, so it will automatically spring back.

And there is a folded part on the front of the tape measure, which works at this time, so that the tape measure is stuck outside, so that it does not fully retract. It was loose at the beginning, but it became tighter when it was pulled out. After letting go, it should have a recovery process, so it will automatically spring back. That is, it was loose in the beginning, and when it was pulled, it tightened, and there was some elasticity between it, and then it would bounce back naturally.