It’s seems not so impressive, but when you think about it, we are constantly keeping a 1,7m tall, 65kg (average) bundle of meat upright, on all surfaces, angles, when moving or standing still. How do we stay upright all the time without even thinking about it?
You have a [“balance” organ](https://www.news-medical.net/image.axd?picture=2013%2F5%2Finner-ear.jpg) that detects gravity (acceleration) inside your inner ears. You also have [proprioception](https://en.wikipedia.org/wiki/Proprioception), your brain knows exactly and continuously the position of all your limbs. And a whole part of your brain called [the cerebellum](https://en.wikipedia.org/wiki/Cerebellum) is responsible for doing all the “calculations” and reactions necessary for your body to stand up, move, run, etc., and for ordering the muscles in your arms and legs and feet to balance and to push at the ground appropriately to keep you in balance.
You don’t think about it because you think with the [cerebral cortex](https://en.wikipedia.org/wiki/Cerebral_cortex), basically a different part of the brain. You can of course control your movements and even focus on standing upright or moving or whatever, but the cerebellum and the balance sensors do their jobs even if you don’t pay attention.
In your ear is a small collection of bones that have fluid in them. They act like spirit levels and your brain is constantly being fed info from them and making tiny adjustments in your posture, stance, movement to keep you upright.