Sri Aurobindo had made it clear to me when I was still in France that this yoga in matter is the most difficult of all. For the other yogas, the paths have been well laid, you know where to tread, how to proceed, what to do in such-and-such a case. But for the yoga of matter, nothing has ever been done, never, so at each moment everything has to be invented. page 357 , Mother's Agenda - volume 1 , 28th Jan. 1960