Dissatisfaction occurs because the mind spins around in such a way that there seems to be no beginning and no end to its motion. Thought processes continue on and on: thoughts of the past, thoughts of the future, thoughts of the present moment. Thoughts are prompted by and also identical with dissatisfaction, the constantly repeated feeling that something is lacking, incomplete in our lives. We are always trying to fill the gap, to make things right. The continuing action of struggle and preoccupation is very irritating and painful. Understanding and confronting suffering is the first step, the First Noble Truth taught by the Buddha.
From “The Four Noble Truths” in Cutting Through Spiritual Materialism by Chögyam Trungpa, page 152