"Whether you believe you can do a thing or not, you're right. "This witty statement can cause confusion at the first read. How can you be right both ways? Of course, Ford tries to emphasize the importance of your beliefs about yourself with respect to your possibilities. He wants to show that above everything else, willpower and attitude is number one thing above everything else. He who believes in himself will act more confidently and with more determination.
If you believe you can pass your exams, you can, because you will not be put down by small mishaps. If you believe you can lose weight, you will not be prone so giving up your diet because you think it will not work or because you don't have the willpower.
Furthermore, he who believes in himself will have a powerful frame that can absorb everyone else into it, making them also believers in your success.
If you believe you can do the job, you can get it because your interviewer will be convinced by your determination. If you think you can start the business you can, because you will make the bank a believer when you comment them your plan. If you think you can get the girl/guy you like, you can, because you will come over as a confident, attractive person.
Believing in what you can do is the first, second and last step you take to achieve anything. Henry Ford knew it, and he changed the world. Do really think you can not achieve something? You should realize you might be completely and utterly wrong. You may be constraining yourself with your beliefs, and thus constraining your achievable reality. Consider this other thought from one of the most successful business men ever and caused a revolution in the auto industry:
"One of the greatest discoveries a man makes, one of his great surprises, is to find he can do what he was afraid he couldn't do. "There are many techniques that try to help you believing in your possibilities, like strong visualization, repetition, self-hypnosis...etc. There are also many techniques about making others believe that you have the confidence in yourself, based on body language, oratory techniques, persuasion, etc. But I find there is often to much focus on the technique itself and forgetting about the goal, which is to make yourself strongly believe in it. This is the seed from which everything else must grow and bloom. Without deep confidence in yourself, everything else is bad make up.