That idea of which we think is not a reality and thus it cannot be object mindfulness. We cannot expect there to be many moments of sati in the beginning. Sati is non-forgetful of the reality which appears now, through one of the six doors, and at that moment understanding of that reality can develop. That kind of understanding is direct understanding of the reality which appears and it is different from theoretical understanding. The development of direct understanding of realities is the development of insight of the Buddha taught.
Insight leads to detachment from the self.
We learn that what we used to take for self are in reality many different elements, namas and rupas, which can be know when they appear. My husband and I had been invited to a restaurant where it was very cold. But that would have been impatience and lack of consideration for our host and hostess. I considered that the namas and rupas which arise are beyond our control. They arise when there a re conditions for their arising.