An unfinished story

There was once an ordinary guy, born in a good family. His childhood was happy and normal. He went to school and made good friends. His parents inculcated good values in him and fulfilled his ordinary desires.
Education was a priority in his home and so the guy did very well in studies. He went to the best schools and eventually the best college. He took the best courses and scored the best marks. There was, however, only one course that remained with him for the rest of his life.
The professor teaching that course was young. Mint fresh returned from the best college in the world. And he was unconventional.
One day he told the class a story - about an ordinary boy who led a normal childhood, was really good in studies, went to the best college, took the best courses, scored the best marks, took up the best job, did well in his profession. The boy in the story always wanted to play tennis for a living, but kept waiting for tomorrow, the next year, the next bonus, the next event. Eventually he was old and could not play any tennis.
After this story the professor turned to the class and gave them a choice - do what you want to do or live with the thought of what-might-have-been.
Our hero was troubled by the story. He could not forget it.
He completed his education and took up the best job. He did well in his profession. But he kept remembering this old story that his professor had told him. It still troubled him, and he did not know why.