I also think of it as a doorway. Some doors are open to you; some are closed. And some doorways you haven't noticed are there. It's fun to notice a doorway - behind a wardrobe; plastered over - for the first time when you return to a place you've visited many times.
But, for me, it's also humbling each time I realize there's more to it. It feels unpleasant at first (I guess that's my ego imagining I know everything), but then it's freeing and reassuring. Nature's imagination is greater than my imagination.
edit Unfortunately, I feel as though I know all the principles, and it's just uninteresting details - data, information - that I lack. I hope this is wrong, but I can't imagine how...