First you really need to be honest with yourself. It is the difference between commitment and involvement. Secondly, start small if you need, in order to boost your self-confidence. Go after things that you know for certain will be attainable and congratulate yourself onthe achievement. This of course leads us to focus.
Concentration is a big source of failure among many people.
My father has a great technique that he uses for his reading. He checks to see how many pages he can read in a book before his mind wanders. Then he checks to see how long it took him to read those pages. Now, whenever he reads something he must focus intensely on, he applies himself in blocks of time based on his measured attention span. This allows him to absorb information at stellar rates, and in his opinion has done quite a bit to actually increase his attention span.