A commonly observed characteristic of transformed consciousness is a fundamentally different perception of time. This perception was fundamental to Eckhart Tolle's The Power Of Now enlightenment. Tolle distinguishes between “Calendar Time” and “Psychological Time”. Calendar time is when one is actually planning something. Psychological time is when one is fantasizing about the future, or the past, and usually with emotional content. Tolle argues that Psychological Time leads to unhappiness, e.g. the past leads to regret and unhappiness, and the future leads to stress, fear, and anxiety.