I think Dogen is talking about perspective here, about where we place our eye and the difference between truth and illusion which is tricky business. What I have been experiencing today as Dharma may not be an exact experience of what Dogen is talking about but I think there is some relation. Today I took my soon to be 94 yr old mother to the doctor. Lately, after much work (years in fact) I thought to myself I am making friends with my mother. She no longer pushes my buttons in the same old way. And then I realized that yes I am making friends with my mother but really I am making friends with myself. I have done enough work on this that I am no longer stirring up trouble, making myself irritated at the things she does. I don't read things in to her every action. I don't take things personally. In short I have come to see the "truth" of how things are. I have come to accept her and myself. We are no longer doing the age old misery tango that we have done for so many years.
I still listen to what she says and think that it has a negative bend to it, that her glass has a hole in the bottom and is more than half empty. And that makes me feel sad for her. But I can see that life can be difficult for those of us with a practice, who spend time reflecting and working with what we do. So how difficult is it when you have nowhere to rest all your troubles and grievances? Today my partner and I could even have a good old laugh about some of her comments, no ranting and grumbling on my part, no need for him to commiserate, just a good old laugh and on with the day. And so there I was in a boat with my mother eating cheese blintzes and poppy seed cake and both of us were enjoying ourselves thoroughly!