We don t need to respond to every stimulus. If we have a thought about a person, we don t have to evaluate that person, or examine our relationship to them, or rehearse a future conversation. If we hear a noise, we don t have to investigate. Thoughts and sensations will come. All we need do is notice them and let them go.
Thoughts are like clouds that appear in the sky.
They don t require us to do anything about them. We can observe them and let them pass. You don t need to classify the cloud, or think about what it looks like. It is just there, and in a little while it won t be there. With persistent practice of letting go of our thoughts, our mind becomes calmer.