One of the most interesting aspects of t'ai chi is the way in which it evolves as we practice. One thinks one has 'figured' something out and then suddenly another shift in awareness happens and everything changes. Lately sinking feels very new to me, it is not that I haven't been sinking, the change is that sinking is happening in me. As soon as I let go and relax into the moment sinking happens. I open to the ground or maybe the ground opens to me. At this subtle level it is impossible (for me) to distinguish. Momentarily the separation dissolves there is no me, no outside, and no inside, just t'ai chi happening.