In saying 'I think, therefore I am', Descartes lifted our identity into the world of our heads. If you cut off your hand, are you still you? If you lose both legs? What makes you you? Is it our thoughts? Do we lose someone when their thoughts start to fade? A division in Eastern and Western philosophy is the role of the body in philosophy. There isn't a separation between the mental and physical. In Vedanta, the philosophical arm of Yoga, everything from exercise, breath, and food to relaxation is fair game. Existence wraps all the connection and relationships. Our identity is all inclusive.
By elevating thought, we can inhibit it. If we prioritise it to the neglect of other things. The broader practice of Yoga also focuses on thought. The stilling of the mind ('Yoga chitta vritti nirodha'). It all starts with being able to sit comfortably. To sit comfortably starts with having control of the body. Having control of the body starts with what you eat, how you move, and learning to relax.
The irony of only focusing on 'the most important thing', is that you may never reach it. The simple things, the basic competencies of life, are the first step on the journey.