Someone once told me that they live by the motto "Always say yes." She said that when she was younger, she wouldn't jump on opportunities because she didn't feel prepared or was too shy. She overcame this and started living by this motto and the most magical things started appearing in her life.
It's also a motto I've taken to heart in life and in business. This doesn't mean that you should say yes to ridiculous or dangerous things, but it does mean that you should say yes to things that might be difficult, thrilling, challenging or intimidating.
What I really learned from that was to take opportunities, don’t waste them and certainly don’t give excuses not to take them.