The only two exceptions have been, when once i was simply scammed. Lesson learned: to never get a partner onboard unless it's done in a way that i hold they keys in a way that he physically can't scam me: always pretend to trust, but never really trust anyone. Especially since people who can't be trusted are those you instinctively trust the most because well, it is their job to get people to trust them. But that could be an eye-opener to some 20 years ago when it happened, but hardly is anymore: the entire world is now a low-trust society, so hardly anyone - even a fresh 25-year old guy i was back then - could make this mistake nowadays.
And the other one, is kind of funny! I made an app that allowed people to back up full hard disk, physical, or logical paritions of any file system supported on Windows back then, and re-create them either 1:1, or turning them into FAT32 partitions, onto any other physical device, if need be, adjusting the size. While building and trying to sell it, i talk to another guy who, at the same time, built a similar app, mine was a lot better than his but he had some fresh ideas so we communicated a lot. After a few weeks, i make several grands of sales and was very happy. But then i had a few refunds because several clients complained on performance (some probably have tried it on damaged file systems, some were real bugs, but no one knows). I felt too bad about making people so upset and after few days of moral struggle, put the app down and quit the whole thing. And the guy who made the other app was the founder of Parallels, he's now a billionaire - the app was Acronis True Image.
For the low trust issue, I think it is becoming more clear with the rise of blatantly fake content online. I think a good lesson could be learned in what formalities you should get in place when working with others to prevent getting screwed over. I myself have been screwed over before by business partners and learned that you really need everything in writing and often lawyers.
For the windows app, did you just not have the time to fix all the issues? Or was it the weight of responsibility in what the app did?
I guess the hardest part about these stories is as they say "hindsight is 20/20"