It's a phrase that Leo emphasizes a lot. That reality as it is appearing in direct experience is exactly as it is. Nothing is hidden. There is no "stuff behind the scenes". There is no such thing as atoms and molecules. There is no mechanism behind it.  All there is are those appearances!. Now from common sense perspective and day to day life this doesn't make any sense. We all function in life knowing that there is way more stuff than just what we perceive on the surface.  Will give  just give one example.. A jar of honey and I will put a drop of poison in it.. If I ask you to eat you won't eat it even tho you can't taste the poison or feel it in any way (except when it starts poisoning you). So just because you can't perceive the poison in any way (all you can perceive is the  delicious honey)  doesn't mean the poison doesn't exist! And that's why you don't eat the poisoned honey.  We can apply the same principle to the "stuff behind the scenes". We don't perceive atoms and molecules and the cells in our bodies but that doesn't mean they are just imagination and concepts!