All ripples start from within and all that you see around you is an expression of that which is going on inside you. If you want to change the way your child is motivated so he (or she) can complete his picture, on paper and in life, then you must first learn how to reach completion yourself before you can transpire this to him. When he becomes tired or bored, show him how to break something down into parts, even if you have to divert his attention from is to re-stimulate his mind. Bring him back to the drawing again shortly after and continue. The only time he will appreciate the idea of completing something as a whole is when he actually reaches that point and feels the joy and gratification of it. The reason why we see so many children failing their education is because they have not been shown the correct procedure of how to learn whilst keeping the mind stimulated. On the contrary, they have not been taught what to do when the mind begins to switch off. Take a rest or try something else, but go back to what you started because if you carry short-lived experiences forward in your life this will begin to grow as a fundamental principle in all areas of life.