A bounce is a physical reaction to a maximum effort.

Let's say you go to the gym every day. On each machine you can solidly do 25 reps.

As you begin to get stronger and in better shape one day you feel especially strong. So instead of your usual 25 you bang out 30 on each and feel like a badass doing it. You've just run a new top!

Next day you feel it more. Bit more stiffness and soreness. Nothing wrong with that. Great to feel that way. However if you went back the following day not only could you not repeat the 30 you'd be hard pressed to return to the old plateau of 25. What happened? You bounced.

When the body does something special and better than ever before it needs more time to recover.

Same with horses except they can't tell their trainer.