What is the most important factor that enables you to achieve a goal after you've identified the goal and developed a plan? You, of course, must execute the plan and you may even have to tweak the plan along the way, but what actually keeps you going, working, step-by-step, per the plan. I think its self discipline.
You have to discipline yourself and take control of yourself and sometimes force yourself to execute the steps in the plan. The people who are at the top of their sport or profession all made themselves study or train on days when they really didn't feel like it, or did even think they would be able to.
What will determine your degree of self discipline is how much you desire to obtain or achieve your goal. There is a strong possibility that you have seen a competition of some sort when a less skilled person or team was able to defeat an opponent considered to be highly talented. This is because the team or person considered to be the underdog had a higher intensity and/or hunger for winning on that day than their more skilled opponent, which usually means the team considered to be the underdog was more prepared for the competition.
So remember, your ability to achieve whatever it is that you are working towards right now, rest in large part on your ability to be discipline. Unfortunately, many continue to struggle with self discipline, and require coaching to keep them on track. This is why so many people hire personal trainers to get in shape. Many of those who get personal trainers already know what exercises to do and how to do them, but they hire trainers nonetheless because they need someone to essentially coach them and hold them accountable. The health and fitness of people with this mindset, is solely dependent on the affordability and accessibility of a good fitness trainer. This is why so many people cannot maintain a healthy lifestyle after they part ways with their trainer. However, the good coaches, trainers, teachers, tutors, etc. will put more focus on teaching their clients on how to obtain the discipline they need to keep them focus and diligently taking the necessary steps to keep them on track, which will allow them to not only achieve the goal at hand but also the goals they set for themselves in the future.