Determination can be described as purpose and resolve. I've never met a great athlete that did not have an intense purpose (win conference, make/win state meet, make the Olympic team, improve), and the resolve to work through the trials and tribulations of training. Training is extremely hard! Not just in the sense of intensity, but in the sense of dealing with disappointment and frustration. Athletes that let disappointment and frustration get in the way of their goals will not succeed! Without determination, success is difficult, if not impossible, to achieve.
Discipline is the systematic instruction intended to train you as an athlete. Basically, your commitment toward your instruction should be more important than the immediate satisfaction of your base desires. Whether it is stretching after every practice, performing a drill prefect every time, going to bed at a decent hour, making sure you eat consistently and healthy throughout the day, great athletes discipline themselves to do the right thing over and over. Discipline enables you to improve consistently! I've known great athletic talents that did not want to discipline themselves, only to see less talented, more disciplined athletes eventually pass them up!
Dedication to your sport is the single minded focus it takes to be great. Distraction are the single biggest reason people don't improve. Improving is about assessment and self-evaluation. Critical and honest self-evaluation is a learning tool! Use it! Dedicated athletes rarely have time for anything else because they love their sport and improving at it. It is this single minded focus that leads to achievement and reward. Without dedication to your sport, it would be impossible to be the best!
The three D's are free to anyone. Most people can understand the three D's, but very few can master them. If you are willing to be determined, disciplined, and dedicated, then you too can have a successful high school athletic career.