All investors have the "fish that got away", mine was investing in Exxon, a year or two before the Exxon Valdes incident, instead of tech stocks,I read too many message boards on how Tesla was bankrupt and never going to succeed, and missed out on buying it at $17. If I would have spent $5k on Tesla stock, it would be worth $176,000 today.
Lately with my investing (play money), I've been using the reverse reddit/message board strategy, which has worked out pretty well so far.