Zen teacher John Daido Loori said,
“[A]ccording to the Buddhist point of view, nonattachment is exactly the opposite of separation.
You need two things in order to have attachment: the thing you’re attaching to, and the person who’s attaching. In nonattachment, on the other hand, there’s unity. There’s unity because there’s nothing to attach to. If you have unified with the whole universe, there’s nothing outside of you, so the notion of attachment becomes absurd. Who will attach to what?”
Because we think we have intrinsic existence within our skin, and what’s outside our skin is “everything else,” that we go through life grabbing for one thing after another to make us feel safe, or to make us happy.