Think of something that you absolutely know without a doubt you can’t do…like singing or walking a tightrope or writing a short story or being a racecar driver or a heart surgeon. Now think about how you “know” that you can’t do it. Were you told as a kid that you couldn’t? Growing up, did you assume from reading about it in a book or looking at it on TV that it was too hard for you to do? That it was simply outside your capabilities? As an adult is it because it’s just too hard to learn something new?
All the reasons above, and any more that you can cite, are wrong. Every single one of them.
The reason—the only reason—why you know you can’t do something is that you truly believe you can’t. Period. Regardless the path to get to that belief, you simply accept as true that it is hardcoded in your DNA and there is nothing you can do to change that. The power of your belief is so strong that it easily overrides reality and the plain and evident truth that is right in front of you. That truth is that if belief is strong enough to stop you from doing something—something that physically or mentally you are quite able to do—then surely that belief must be strong enough to allow you to do those very same things.
What is the difference between knowing you can and knowing you can’t?
Believe. Go. Do.