My crazy story is more of a slow burn than one white-hot moment. I acquired roughly 250,000 sports cards roughly 20 years ago.
These were the "common boxes" from a store that was changing owners. The old guy had a habit of breaking boxes for the hits. The new guy was going in more of a Pokemon card / Hallmark store direction and didn't want mountains of cardboard laying around.
If you've ever moved ~50 monster boxes of cards into your house, you know how bat-shit crazy this truly is. I went through them, one at a time. I pulled some decent singles from there; however, nothing earth-shattering. After I finished with each box, I would top it off with more commons and sell it on eBay.
Probably wound up with roughly $2,000 and about the same amount of value in singles I kept. It only took about a year (1 box per week) and about 50 trips to the Post Office.