"Personal interests" typically refers to a person's true passions, the arts or activities that they would do every day if they could. These are often placed in contrast with "professional interests," a person's ambitions within the traditional professions and careers in modern society. Professional interests keep the bills paid and food on the table; personal interests get us out of bed in the morning.
For many young professionals, their ideal job would be a combination of their personal and professional interests. It is certainly difficult to make a living doing what you love, especially if that happens to be an artistic or nontraditional endeavor. However, for many people, a life without their personal interest would be unbearable. In this case, it is essential to pursue it with vigor. Other people can be content working at a job that isn't exactly their passion while pursuing their personal interests on the side.
It is not a good idea to pursue your personal interests if doing so would come at the expense of the health and happiness of those around you. For instance, when one becomes a parent, that often involves putting aside personal interests for a time so that the parent can provide effective care for the child. It would not be very responsible for a new parent to take off on a cross-country road trip with their band, for instance.
It is certainly possible to achieve success in the field of your personal interest but not feel satisfaction. The comedian Amy Schumer dedicated herself to her personal interest for years, working as a waitress in New York City while pursuing her dreams of stand-up comedy stardom. In the mid-2010s, she achieved her goal. She produced four seasons of her hit television show and starred in three major motion pictures. She said, however, that achieving her goals had a negligible impact on her overall well-being: "I'm the same amount of happy as when I was waiting tables," she said in 2017. For some people, happiness is not tied to either their personal or professional interests. It is based on their health, sense of self, and outlook on life.