NOW, because...

You can think about the Future, but that's all you can do with it - mainly because the only thing real about the Future is your thoughts of it.
And you can think about the Past - we call that Memories - but that's all you can do with it as well.

But you can't think about NOW. You can thnk about it before it happens, or after, but that non-point-in-time we call NOW? All you can do with it is DO something.

NOW is the domain of action.