We may believe in one or the other of the philosophies of Dualism or Non-Dualism. We may see these philosophies as either contradictory or complementary.
However, when we want food or sex, or feel threatened, we automatically respond from Dualism, not Non-Dualism. If we watch a person die, or look at a corpse, are we not all struck by the mystery of apparent matter and consciousness? The higher truth quickly goes out the window in such moments and we find we are faced squarely with the Dualistic, conditioned response of the stuff of our mind.
There is something between us and Truth, the Absolute Reality, and that is called the mind. Training the mind is the starting point for Patanjali, in the Yoga Sutras. For example, one of the first things he talks about is observing which of our thoughts are useful or not useful, positive or negative. Then he directs us to learn to make choices in life on the basis of what is positive and helpful in our growth, choosing to do that which we know leads towards a stable, inner state of tranquility. Such self-observation, self-examination, and self-training are necessary in preparation for the deeper practices.
The Dualism of the Yoga Sutra gives us detailed instructions on how to clear away the clutter so we can find the door. Non-Dualistic Vedanta philosophy gives us a sound contemplative base for deeper understanding of the nature of the door and that which is beyond. Tantra shows us how to open the door, as well as how and where to knock.
To view these as contradictory leads to confusion. To view them as complementary leads to freedom. We can apply the Dualistic and Non-Dualistic philosophies as different aspects of the same one journey within, which eventually leads to the direct experience of the center of consciousness, wherein all these questions are resolved and dissolved.