Dr. Courtney said:
I picked Physics, because I loved it deeply. I remember checking out books from the elementary school library on light and relativity. In 6th grade I was sure Einstein was wrong because (more or less) I had re-invented Galilean relativity. It was not until college (Modern Physics) that I realized Einstein really was right. My Mom also supported my love for science by buying tons of books. I remember being excited when the new Funk and Wagnalls science yearbook.
My Dad always had wanted me to be an engineer. He had been an engineering major before switching to business, because engineering was too hard. He was something of a party guy in college. His parents tried to use their financial support to change his behavior, so he joined ROTC (with a free tour of Vietnam) to achieve financial independence and freedom of lifestyle. My parents met in a Physics class at LSU when my Mom struck up a conversation about beer, a subject in which my Dad was an expert. In any case, my Dad favored engineering, because he knew I would make a good living in it. Since I had done well in high school chemistry (winning some awards my Dad was proud of), my Dad leaned toward Chemical Engineering. Growing up with the petrochemical industry we both knew a lot of Chemical Engineers and jobs were literally everywhere.
Even though what you write on the admissions application is not binding, I didn't want to go against my Dad's wishes, so I called and asked him if I could write Physics in as my "intended major" instead of Chem E. Deep down it was my true love. It's not that I wanted to be a Physicist, it was that I already was one. I deeply longed to know the fundamental laws of nature, how light and atoms worked, what Einstein had really meant, etc. I had no confidence that I could actually contribute to science myself, but I deeply wanted to do Physics rather than just make/design stuff.
It was my deep desire that helped me push through when the math and coursework got really hard. I could not have persevered had I been in it for money rather than for love. A couple months after I was admitted to LSU, I was invited to some reception, where one of the Physics professors met me. Over the next 18 months, I met a number of Physics faculty, and they cemented my impression that this is what I wanted to be. Of course, they had personality quirks that turned me off, but I loved how they _thought_. They had beautiful minds. I wanted to think like them.
I didn't know many (non Chem) engineers growing up, but my girlfriend's Dad had been an engineer (Mech), and he kinda turned me off to it. Too much focus on stuff (cars, money), and no real passion for science that I could see.
Out of grad school, my first two jobs were engineering jobs. My starting salary may have been close to BS Engineers, but my PhD research had given me enough experimental skills and mathematical and problem solving prowess, that I quickly advanced to a Senior and then to a Principal Engineer with commensurate increases in salary. I was well into six figures before 35. But after I paid off the mortgage on my home, Engineering got boring for me, so I transitioned to a faculty position and started a small company on the side to pursue research interests.