Many individuals make it impossible for themselves to find happiness (enjoyment) in the present moment by choosing to focus their attention on the past. Their depression, resentful hostility, or guilt pangs are all kept alive by their mentally dwelling in the past, a past that no longer exists."
Other people keep focusing on the future and, as a result deprive themselves of all satisfaction with the present moment. They spoil it by worrying about what might go wrong in days or years ahead.
A third and enormous group of people have learned to spoil the present moment without looking ahead or back; they just focus on what is not rather than what is. They want what does not exist, they want it now, and they feel entitled to it.