It is always NOW. It is never then, but our mind seems to get confused with what we didn't like in the past and tries to control how things will turn out in the future. This takes our attention away from the only place life really exists, which is in the ever evolving moment of NOW.
When we push away what we feel in our body, or judge something that is happening, or judge what another person is doing because we don't like it, we are practicing resistance to life, which is THE CAUSE OF STRESS.
Imagine trying to resist something that is. Imagine pushing it away, and trying to make it something else. When we do that we are just supporting the practice of dissatisfaction and unhappiness. We then begin to act more and more from those kinds of subconscious programs and create perception filters who's only purpose is to push away everything that may be a threat to happiness. The problem is that once we get caught on that ride, we become so focused on the potential of unhappiness in every thing we see through those fear perceptions, that we miss what is happening right now! What is happening right now is the only life we get, and if we are always trying to reject it with judgement or a better idea than what is, then what is happening now becomes pushed away and we live in perpetual fear of potential unhappiness!
it takes a lot of energy to always push away things that are real (the present moment) for something that is not real (the resistant thoughts and programs in our subconscious mind that are rejecting it). Of COURSE THE RESULTING EXPERIENCE IS STRESS! Because distance and numbing and walls are created between "what is" and our thoughts of what should or should not be. The amount of resistance we are putting up is in equal proportion to the experience of stress and tension that results from it.
The solution is simple! Just allow, accept, and embrace life as it is! and learn to sit with the feelings and emotions that arise from doing this.... then there is nothing to resist or create stress from.