The Harvard student need not go to grad school to just continue his major at the graduate level. There are professional degrees - law and medicine are just two. Others mentioned MBA after two or three years. There are also Masters in Public Health, Public Policy, Social Work, Dentistry, Vet, City Planning, Architecture - you get the idea. People entering these programs may have majored in history/English/psych. If the student isn’t sure what he wants to do, working is a good option, even as a secretary or office manager, for a few years.