"Whether you believe you can do a thing or not, you are right."
Henry Ford was the one that provided the previous statement, and it's been published so many times in so many different books, that I can't really remember where I first read it. Regardless of the exact source, what he says is totally true -- if you convince yourself that you cannot do something, you will not do it, while if you convince yourself you can do something, you will try (and usually succed) in doing it.
Is this a business quote? I don't know. I would answer that question with a question: Is it not a business quote?
I think one of the biggest mistakes that people in business make is to underestimate their ability to do something and usually convince themselves that they cannot do it. It's all really a mind game. I like people who fly in the face of what others believe that they can't do in a particular position in a company. There need to be people that challenge the "rules" that are pushed down upon them. Further more, people need to be willing to break through their own bounded reality of their capabilities and convince themsleves that they can do the work that is set in front of them.
Throughout my life I have found that it is so much easier for people to say "I can't." Why is that? What if we did not allow the conjugation of the words "can" and "not?" That would certainly make "I can't" a little more difficult to physically say, maybe make people think twice?
I love working in companies that are very unstructured (i.e., do not resemble the military command and control structure). Some people thrive in unstructured companies, while other people simply collapse. One thing you very rarely hear (for a long period of time, at least) in an unstructured company is that someone "can't" do something. It's almost as if the "can't-do" attitude has been banned, and if you have someone in the company that consistently "can't-do," they simply die of attrition -- after all, no one (especially in an unstructured organization, where you sink or swim based on your own ability to convince yourself that you can swim) wants to work with someone that can't do.