Out of undergrad I was recruited by a major defense contractor and selected for a leadership development program. Aside from making me fly various places and do nothing they also made me do nothing at my "home" desk in a secure facility (so no cell phone or playful browsing) by myself.

I found a bunch of old math texts and starting reading them and doing practice problems out of sheer boredom. It was then without the stress of juggling other subjects and exams that I realized I actually liked math and just had terrible teachers for most of my education. I went through Calc I,II, III in the first month or two (some was review) and by the time I quit about a year later I had enough momentum and interest to go through differential equations, linear algebra, some analysis, and more advanced matrix methods.

It was one of my favorite jobs.