I did an internship in a small advertising office in high school, which taught me that I definitely did not want to go into that field. It was intensely boring. (yeah, I recognise that advertising probably also has exciting flashy jobs but there's a lot of market research and even the exciting creative bits were just... Not for me.)

By contrast, waitressing and working on a farm were both enjoyable, albeit not remotely the direction I went for long term (engineering...)