Could it be that what he meant was degree to which we let our spirit live detached from the form we embody?
Attachments are a sure way to close the door to opportunities!
And just to make sure, there is a fundamental difference between the doors closed by the will of Higher power and those we close ourselves because we think we know better.
We attach to people, places, experiences, expectations as well as possibilities and results!
Attachments are thieves. They take our playfulness, spirit of curiosity and exploration, and inspiration for whatever it is we need to do with the time we chose here.
"Be open to everything and attached to nothing."
We all are spirits, living off the sense of freedom within a form we take. Knowing and experiencing that everyone of us is that freedom and not really a form which inevitably changes is living in the Kindgom of Heaven.
Attachments are everything that bounds our formless spirit to the form that is temporary and changing constantly. So how can we define ourselves, our hopes, and our life paths based on that which is visible to the world.
Because as soon as the moment passes, if attached to it, our spirit experiences grief, loss, jealousy, emptiness, loneliness, disconnectedness...when it should feel gratitude, expansion, and contentment.
Separation is not part of the deal with the Universe!
So far, I met two men in my life who left me feel more loved and less attached to that love at the same time, their approach nurtured the freedom of my spirit. And I met them both for only a day. They left, I left, and we all allowed the other to take what they needed without the need to hold on to it. Love is expansion! And leaving is part of that for us to realize it fully!
These days we call these realizations MIRACLES!
"Miracles occur naturally as expressions of love.
Miracles are natural. When they don't occur something has gone wrong.
Miracles represent freedom from fears.
A miracle is never lost!"
A Course in Miracles
PS. personally, this is my greatest lesson so far and greatest joy to my spirit!