I'll start with one of mine, possibly a bit controversial, as the success we are talking about materialised in giving up on an idea that wasn't going anywhere.
A few years back, along with my current co-founder at Morgen.so, we were toying around with (you gessed it) a dieting app! It's been thrilling, and exciting, but after months we were getting nowhere, the product was great, but we realised not even us were power users, so after making a very thourough pass on all we have done up to that point we decided to terminate the project.
Sometimes, success doesn't materialize in traditional ways, sometimes, it's just a matter of being able to move on, freeing your mind and tim for what's next!
What's your story?