'There is a crack in every thing
That's how the light gets in'.

I think he got that from Rumi or some other poet. He had the wit to realise how valuable that perception was. I thought he meant we see something important through a flaw in its make-up. Now I'm not sure. It might mean there is a very tiny conduit in the nature of every thing that if realised and used, opens a world of understanding. Here's a related idea from William Blake's The Marriage of Heaven and Hell:

“If the doors of perception were cleansed every thing would appear to man as it is, Infinite. For man has closed himself up, till he sees all things thro' narrow chinks of his cavern.”