[throwawaymath]

The irony here is that you're asking how to use an essay about avoiding self-absorption in order to accomplish your goals more efficiently. It's not about your goal when you're in a grocery store, it's about the fact that you can't focus on anything other than your goal.

The idea is not that there's a profound insight hidden in there. In fact, the essay repeats several times that there's no trite lesson or platitude to walk away with, and that the basic idea is already obvious - the world doesn't revolve around any given person. What's not obvious is exerting the mental effort to consider that fact when you feel like you're the only person who has any self-awareness in a crowded grocery store.

On a more practical level, if you're looking for a lesson then this is close to it - you get in your own way, intellectually speaking, by defaulting to the easy path of discounting the myriad reasons for other peoples' behavior while rationalizing your own. We tend not to think about the things that are so obvious they're dreadfully mundane, but because of that we close ourselves off to insights that could be very helpful but for the fact that we're locked into our first-person perspective.

More succinctly: if you find yourself thinking that you're surrounded by people who lack self-awareness, you might be lacking some of it yourself.