Ask HN: Stories of startup persistence

I've recently closed the doors on my 6th bootstrapped startup in 15 years. This is in addition to many, many side projects that i wouldn't​ consider calling a startup. I've never been able to find product/market fit. I'm getting better, and thanks to ideas from lean startup, each attempt is taking less time and resources, but i cant help but wonder if I'm cut out for this. Are there any examples of founders who tried and failed multiple times before getting their big success?