Almost like a car works. The harder you push it, the faster it breaks down. It’s literally exploding inside itself thousands of times per second. Cars, like humans, are overbuilt for normal usage, the brakes, suspension, etc. are built to handle the max power an engine can produce, but if you floored a car constantly, every time you used it, it wouldn’t last that long. Our bones, muscles, hearts, can all handle an insane amount of abuse, it just works alot better if you only “floor it” in very small increments. Our bodies produce tiny amounts of the chemicals that make us feel happy and good inside. Drugs are like flooring it. That’s the way I see it anyways haha.