If your dream is something that can be achieved by hard work rather than luck or being a statistical outlier then go for it, especially if it gives you a livelihood.

Another idea is to time box it. Dedicate every fiber in you to it for a fixed amount of time and at the end of that truly evaluate your odds. This kind of dedicated application and focus does transfer into other areas.

When it comes to sports, you are only young once and school and a vocation will always be there. But have an exit plan and a hard cutoff where you really evaluate your trajectory.

If you have a dream and a well defined purpose that fills you with passion don't throw it away casually. It is a rare thing to know exactly what you want. Figure out a way if you can.

For the rest that can't determine their dream, choose goals and paths that give you the most options at their end. Don't decide what you are going to be for the rest of your life, pick a place you want to be at in three to five years and shoot for this.