system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why it takes so long for humans to gain lean muscle mass.
gpt
If you don't like spending more money than you have to, you'll only buy a car big enough for your needs.

A bigger car is more expensive, and uses a lot more gasoline than a little car. You wouldn't buy a big SUV if you didn't need it.

Lean muscle mass burns energy - it's expensive for our bodies to build it, and keep it going.

Our bodies won't build muscle unless it's needed. So if you don't have a physical job, big muscles are a waste (as far as your body thinks).

Our bodies are geared towards **survival** above all else.