I think here Napoleon Hill is referring to the satisfaction of that smaller,egoic part of our being where our wants and needs come from a materialistic perspective only. When we are satisfying our Higher Self, we are seeing things from a greater perspective and are in fact satisfying the Whole or using the accumulation of wealth and riches for the greater good of all. We are no longer being selfish to merely satisfy our own materialistic wants but are being selfish to help the growth and expansion of others.

I think it also might refer to "small thinking" where one is easily satisfied with little and doesn't aspire to much else. e.g., the type of people who say, "Well I don't have much in this world, but I am pretty happy with what I have, I am satisfied." when in fact they have a a pretty limited life. I would also read that type of thinking into this paragraph.