The Buddhist concept of attachment:
Zen teacher John Daido Loori said,

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p>Non-attachment is exactly the opposite of separation. Two things are required for attachment: the thing you’re attaching to, and the person who’s attaching. Nonattachment means 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?”

I love this concept. Loori went on to note:

Because we think we have intrinsic existence within our skin, and what’s outside our skin is “everything else,” we go through life grabbing for one thing after another to make us feel safe, or to make us happy.