You as a researcher is the most important instrument in your research journey. You are going to spend a considerable amount of time with your research. If you are not interested in your subject, pursuing any journey will be for the only namesake. Hence, The subject should belong to your area of expertise. Next, the motive of research varies from person to person. One researcher might be interested in solving the problems the society is suffering from. That of another might be interested in adding knowledge to academia. Still, some other researcher might be interested in acquiring a degree.