Re: How do you train/achieve nothingness?
I actually don't really have anything more to add, as all of you have explained it so well.
Just as an end note:
At the end of my journal, I made a note that, "I am guilty of making my own conventions"
The things that I have said here is how I materialized a concept which really could not be materialized, at least in the relative sense. To me it's just a starting point.
As Kevin, Larry, and Mike discussed, meditation, dynamic or static in nature, will lead us to quickly understand this concept of "no-thing-ness".
As Seiser-san said, mushin falls into "let", so we do need to just... accept it.