How do these psychological fears arise? What is their origin? That is the issue. There is the fear of something that happened yesterday; the fear of something that might happen later on today or tomorrow. There is the fear of what we have known, and there is the fear of the unknown, which is tomorrow. One can see for oneself very clearly that fear arises through the structure of thought—through thinking about that which happened yesterday of which one is afraid, or through thinking about the future. Right? Thought breeds fear, doesn’t it? Please let us be quite sure; do not accept what the speaker is saying; be absolutely sure for yourself as to whether thought is the origin of fear.

– Krishnamurti, The Flight of the Eagle, p 12