In the 'ones that got away' category, I had some Amgen (AMGN) back in the mid 1980s when they were just starting out. It went up 30% so I gleefully took profits. I figured out later that those shares would now be worth in the gazillions. Instead, I took the 30% profit and lost most of it in another bio stock. Dumb, but who knew??
As Buffett says --> know your circle of competency. The circle can be widened / broadened via knowledge and experience, but I figure avoiding an overly cavalier attitude toward money is the best way to stay out of trouble, and having a sensible asset allocation model is key. Penny stocks I would forget about completely, but some microcaps can be fun to follow -
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