One day, when I was a student, I asked Andy Yao why he was doing research. As best as I remember, this is what he answered:
-"I need a long-term goal to drive my interest in the field. If the P vs. NP question was resolved tomorrow, I would probably change fields."
I insisted: what did he enjoy the most about doing research?
-"I enjoy the moment right after I have discovered something new. At that time, there is something that I know and that no one else knows yet. It's like being the first person ever to get to the top of a mountain. I spend a few days savoring the feeling."