That which is aware.
With mindfulness, you begin to realize that there is no thought that rises into consciousness that doesn’t have some tinge of liking or not liking something. That doesn’t have some judgement about an experience—either past or future—being pleasant or not. Otherwise, it is unlikely the thought would have arisen in the first place. It is very empowering to be able to see that. As Sam Harris so beautifully says:
“It is quite revolutionary to be aware that liking and not liking an experience is a separable component of the experience. And that you need not always in every case be taken in by it. That is a remarkable insight into the nature and plasticity of consciousness. One thing that training in mindfulness can show you is that which is aware of unpleasant sensation is the same and feels the same as that which is aware of pleasant sensation.
“There really is a kind of equanimity, intrinsic to consciousness that can be quite liberating to discover. And if it's appropriate to say there is a goal to this practice that is pretty close to the center of it; to simply give up this automatic struggle we live with moment by moment, and acquire an ability to leave things as they are, if only for moments at a time. To punctuate our relentless search for happiness, with real equipoise and well-being. To give up the search, by merely paying attention.”