I made 17.5k doing this by dumb luck.
I was trading crypto back in 2016-2017. Making a few thousand here and there. Mostly just from time in the market during the run-up of ethereum. The whole thing drove me crazy because I thought it was so stupid, like gambling. So in 2017 I withdrew my several thousand dollars and put in a trade on coinbase pro for 5 etherum at $100. (I had left $500 to do this, the most I was willing to risk at the time) On 2018-11-25 this trade was executed in a flash crash.
I had totally forgotten about this trade and when I was going to buy a house in 2021 I was looking for any change in the seat cushions thinking I may have left a small amount in these accounts. Well imagine my shock when the amount was just short of $18,000.