When you're flipping or twisting (or both!) it is very disorienting to the human brain. When training new flips and twists, you need external cues to learn how it feels to complete the trick correctly. (In diving, a coach yells "OUT" and you kick your body straight and pray).
Once you've practiced a trick enough, you develop the neural pathways that create kinesthesia which leads to muscle memory. Your brain remembers how your body feels doing the trick and you gain air awareness.
Think about something that took you a while to learn and required a lot of concentration at the time to get it right, but now is second nature. Driving a car is a good example (especially stick!)
Suddenly, in the middle of driving on the freeway, right as you need to complete a tricky merge, you have totally lost your muscle memory of how to drive a car. You have to focus on making you foot press the pedal at the right angle, turn the steering wheel just so, shift gears..
It's terrifying. You're moving way too fast, you're totally lost, you're trying to THINK but you know you don't usually have to think to do these maneuvers, you just feel them and do them.
The twisties are like this, and often happen under pressure. You're working so hard to get it right that you stop trusting your muscle memory. You're getting lost in the air, second guessing your instincts, overthinking every movement.
It's not only scary and unnerving, it's incredibly dangerous even if you're doing basic gymnastics. The level of skills Simone throws combined with the height and power she gets can lead to catastrophic injury if you're not confident and connected to your kinesthesia.
This isn't as easy to fix as just sleeping it off and hoping for a better day tomorrow. It can look like retraining entire routines and tricks. I never mastered my front 1.5 with a full twist because I'd get the twisties and it would mess with my other twisting dives.
So. When Simone says she's taking it day by day, this is why. She's not soft. She didn't choke. She isn't giving up. It's a phenomenon every gymnast and diver has experienced and she happens to be experiencing it at the Olympics. Can you imagine the frustration? The heartbreak?
I'll also add that
@Simone_Biles choosing to bow out pushes back against a dark narrative in gymnastics that you sacrifice yourself for the sake of the sport; you are the product of your coaches and you owe them wins, no matter the personal cost.
No. You owe nobody anything, and you especially don't owe them your body, your health, or your autonomy. I hope every single tiny baby gymnast got that message on self advocacy and setting boundaries loud and clear. Thank you,
@Simone_Biles.