Argh. Buddhist philosophy is ususally horribly written (in the west). Much easier to come to grips with this idea if we start from the much more commonly agreed that our sense perceptions and memory are generally sufficient for survival, but very much inexact in comparison to the reality of what is perceived and remembered.
Add to this, a very strong insistence that everything is in a perpetual state of flux, that there is no perpetual "you" or "me" (or indeed anything). Trivial physical example - a molecule in your body is exhaled, and now inhaled by me... (cue "we are all one..."). A part of the earth turns into a banana plant, you eat the banana, and the banana turns into a human being. Now where are the boundaries of "you" and "the Earth"? See first paragraph reminding you about the very limited nature of your sense perceptions and memories.
The foregoing is stuff "we all know" but push into the background while we "get on with real life", but the yogic/Buddhist approach asks us to foreground it, and ask ourselves how we would conceive of and live life with those understandings in the foreground. Further, what if dynamics beyond those limited senses were at play? Psychology and ethics which takes the above as a starting point, rather than exisiting power relations, ends up looking different from what we have now.