The #1 reason people do not reach a goal is because they slack off part-way, and allow their old habits to kick back into full gear. A goal is something that you strive toward, and in doing so, will make you into a better person.
A goal that you know how to reach is not a good goal. You should aim high in setting goals. This will end up developing you into a far greater being than you would have conceived possible. Not only will you have the immense gratification of eventually reaching your goal, but you will have also grown into a far more advanced individual, and you will be gaining much more pleasing results on a consistent basis. Your habits will probably change, your happiness will increase, and you will begin living a much better life having reached your goals.