We cannot know what is going to happen in the next moment, yet our very existence depends on assumptions about it. Experience is nothing but memory, but it enables the global community to develop. However the fact remains, we do not know the imminently arising moment.
Unknowingly, we correctly assume that we don't know, whilst incorrectly thinking that we do, and thus unknowingly make efforts to arrange our knowledge base so as to manage selected projections in line with expectation. This very effort is a disturbance of the heart's essential pure state, is at variance with the way things are, and thus is a source of conflict. In the normal course of practice, we may well experience an occasional, brief respite from this stress, and be suitably impressed with that result, but the root cause could easily escape our awareness for eons to come.
At this level Dukkha is a subtle boredom: a dissatisfaction resulting from assumptions that the immediate future is knowable. This is enough to keep us separated from the transcendent quality of the present moment.
There is a need to investigate this not knowing, that we don't know about, by carefully focusing on it's resulting stress: Dukkha. Only when it is perfectly clear that we do not and cannot know, will we skilfully find the essence of the "here and now": that limitless eternity of the present moment.