I'll give you two....
A long time ago: 3DO. Video game company headed by Trip Hawkins. I loved their multi-game arcade machines back in the day, but by the time I was investing, they were highly dependent on the "Army Men" game franchise, and put out a bunch of crap. Trip lost his shirt, too, so at least it wasn't saving management at the cost of investors. (he could afford it, though) Gaming, like all entertainment, is a hit-driven business. I learned a lot about making sure I knew the product. (I had heard of, but not played, Army Men) I have and do own video games and entertainment stocks now, but do much more to keep on top of what they are doing. Buy what you know! Great product is a necessary, but not in itself sufficient, part of a successful business.
The other stinker was HQ Sustainable Maritime, a Chinese tilapia farming outfit. They had real product, even made its way back to Walmart. But in the end, they fabricated a lot of their success, like a lot of Chinese agriculture / food processors at the time. Didn't put a lot into it, but avoid Chinese companies like the plague, even with their success to date and future potential. There is no check by investigative journalism / short sellers in Chinese markets to serve as a check to company or government numbers, so that's a game I don't want to play.