Thinking, or more precisely identification with thinking, gives rise to and maintains the ego, which, in our Western society in particular, is out of control. It believes it is real and tries hard to maintain its supremacy. Negative states of mind, such as anger, resentment, fear, envy, and jealousy, are products of the ego.
Eckhart TolleTo be identified with your mind is to be trapped in time: the compulsion to live almost exclusively through memory and anticipation. This creates an endless preoccupation with past and future and an unwillingness to honor and acknowledge the present moment and allow it to be. The compulsion arises because the past gives you an identity and the future holds the promise of salvation, of fulfillment in whatever form. Both are illusions.
Eckhart TolleA built-in reminder is the simple understanding that whenever any kind of unhappiness arises, you know you've lost the now. That's a built-in alarm clock. The moment you realize you've lost the now, come back to the now.
Eckhart Tolle