Not to be able to stop thinking is a dreadful affliction, but we don't realize this because almost everyone is suffering from it, so it is considered normal. This incessant mental noise prevents you from finding that realm of inner stillness that is inseparable from Being.
Eckhart Tolle (2001). “Practicing the Power of Now: Essential Teachings, Meditations, and Exercises from the Power of Now”, p.17, New World Library