system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why can't humans hold themselves perfectly still without twitching, hence the difficulty of the game "operation"?

I don't understand why we twitch slightly holding tweezers, standing still, etc.
gpt
Muscles are composed of many strands. When your arm is held up, not all fibers are being used simultaneously, as that would need you to carry an extra weight. Over time fibers get tenuous, needing to relax, so your they switch  to other strands, and this switch is usually abrupt, so our arm twitches a bit.