Phyllis Diller was a middle-aged housewife in the 1950’s…how easy it would have been for her to say I’m a middle-aged housewife; there’s no way I could ever become a stand-up comic. But of course she didn’t accept that unfounded, limiting belief, and went on to become an icon of American comedy.

ON THE OTHER HAND, the limitations of human physiology are very real. It’s not a self-limiting belief that prevents me from running a mile in 3 minutes; it’s the fact that that’s physically impossible for me as a middle-aged guy with bad knees, bearing in mind that the world record is something like 3:47.

That’s an extreme example, granted. But not everyone has the innate capacity to be a successful comedian, or a doctor, or a chess champion. The simple truth is that we’re always confronted with the challenge of assessing whether our limiting belief is rational or irrational. If I want to try being a professional comedian on my own time, that’s fine because failure means little more an embarassment. If I quit my job to pursue it, then failure means bankruptcy and home foreclosure.