"Seeing is believing" or "I'll believe it when I see it" two strong statements that can make all the difference when it comes to the body. Many people get discouraged because they don't "see" progress, whether it is losing weight or gaining mass.
People who are successful are that way not just because of drive but because they visualized what they wanted. A car, house, weight loss, bigger biceps, it all starts with visualization. In your mind if you visualize what you want you can attain it. If you visualize yourself growing bigger for muscle mass, your mind says "yes I am bigger" and you will start to get bigger with your training. The same is true if you are trying to lose weight. Imagine yourself thin and your body will start to create that reality. Your mind will make your body do the work. Goals can be attained.
The mind is very powerful, it can create and it can destroy. Everything and who we are, are all created by our minds. Positive thoughts can create, and conversely negative thoughts can destroy. When the positive thoughts outnumber the negative that's when you can achieve goals.
Bottom line: visualization of goals in a positive way will create the desire from the body to reach those goals. Good luck and positive thoughts.