An interesting topic.Well, from a recent experience, life has thought me how "dense" I was regarding how opportunities in life and how they can come and go.
Even if the experience was coincidental and I'm being pretentious, the interpretation that I was left with was one which could impact my life positively if I choose to use it. Essentially I was put in a situation where, I saw life as containing opportunities or doors if you like, you either see them or you don't. And if you're able to see them, you can either take those opportunities or walk through those doors or not - through fear. But, if you stall and do nothing... some of those doors if not all of them will eventually disappear/close.