Not a pilot but,
During my spotter phase at Newcastle in the 1960s, I found it was my commercial sensitivities which were waking up, rather than any urge to fly. I used to count the passengers onto the London-bound Ambassadors and work out the load factor (times 100, divide by 55) or more pertinently look at the four or five who boarded the Dan-Air Dakota to Kristiansand and wonder how the hell it could ever make money.
Still doing it for a living, 40+ years later.