system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are we able to stand up and balance on two feet easily, but it's hard to balance on only one foot?
gpt
It's a skill, let's say standing wasn't a thing that you do normally so you will have to face the same issues​ as standing on one leg (different of course).

Quick explanation about how you gain a skill (standing, handatand, riding a bike):

You just need to do it, time after time and each time you are improving your motion and strength your muscles for that position/movement.
And when finally succeeding, unconsciously you work on smoothing it up to use less energy spending for the action - this keep going and going.

There is a lot of info about how the brain really does it if you're interested in that.