Non-reactivity is something you can practice while you’re sitting alone, as sounds, thoughts, feelings, and sensations come and go.
You can choose not to fight them; to roll with them; to feel them fully yet not cling or react to them.
You can keep sitting still, breathing calmly, and focus on getting back to silence after any initial waves of tension or discomfort pass.
After you’ve practiced this for awhile alone, or even right away, you can begin practicing this in daily life.
The moment you feel your heart rate rising, your palms sweating, or your stomach turning in any situation, you may better be able to notice that those are sensations just like the sounds of a bird chirping, and you should feel them – but not react to them.
Once they have passed, you can respond.
But a response is not a reaction. A response is part of being non-reactive.