Chatting with friends or their kids, I often got asked if I liked my PhD study. They tried to figure out if PhD is worthwhile for them or their kids to pursue.

I liked it a lot because: 1) I had a great relationship with my professor. 2) I published often. 3) I traveled a lot, to carry experiments in national labs, to present in conferences, to visit universities and other research groups. 4) My living cost was low, and I enjoyed my lifestyle.

As a matter of fact, in any career, these 4 things (working with great leaders; being productive; expanding a professional network; maintaining positive cash flow) can lead to a happy life.