In Karate there is an image that’s used to define the position of perfect readiness: “mind like water“. Imagine throwing a pebble into a still pond. How does the water respond? The answer is, totally appropriately to the force and mass of the input; then it returns to calm. It doesn’t overreact or underreact.
Clearing the mind and being flexible are key.
Anything that causes you to overreact or underreact can control you, and often does.