If you get carried away by the circumstances "you are not thinking"
If you get carried away by the swings of adversity and do not act or react, in reality, you are not thinking. It is the emotions that carry you, they the ones that drag you like a leaf that hits the wind. If you allow others to decide for you in those circumstances, you are neither acting nor thinking, it will be the will of others that you choose in your place. And all this is neither good nor recommended.
Knowing how to react is putting up resistance at first, looking in perspective and calm and then deciding and acting. It is going against the wind and seeing face to face the difficulties to know what they look like, what they want and what are their weak points.
Reacting boldly and wisely requires more than just courage. It implies being responsible for oneself, managing fear and evaluating what type of response we should apply to the challenge we have before us.
Knowing how to react to what happens to us is avoiding acting on impulse
William James said that there are many people who "think they think", but in reality they only act on impulse. Letting ourselves be carried away by these unthoughtful reactions brings out the worst in us. After all, whoever does not think, who does not meditate on things, ends up making use of the prejudices, beliefs that others inculcate in him and that one simply assumes without protesting.
Knowing how to react involves making the effort to think and reason in a relaxed way to have greater mental clarity. In our hurried world, full of stimuli and pressures, we hardly have time for these delicate and necessary mental processes.
Often it is our own anxiety that makes us end up reacting on impulse, shaping poorly adjusted behaviors that we later regret. Knowing how to react is knowing how to respond from an interior that chooses not to get carried away by those emotions that "kidnap" us at a given moment.