I think that we make our own luck. I read an amazing article in New Scientist a few years ago about lucky and unlucky people. They got people who considered themselves lucky and people who considered themselves unlucky. Then they presented them all with a bunch of hypothetical scenarios and asked what they would do. The people who considered themselves lucky found ways to exploit oppurtunities and saw the scenarios as positive. The people who considered themselves unlucky viewed the scenarios in a more negative light and failed to notice ways that they could benefit from them.

I think that the point he makes about taking control of your reactions is very relevant - you may have no control over your inability to hold a note but you can choose to accept that, enjoy singing in the local choir and get on with finding another career that makes you happy or you can spend the rest of your life struggling to make it as an opera singer and bemoaning your bad luck.