I have encountered lots and lots of problems I could not solve. One of my supervisors once told me that research is 1% inspiration and 99% perspiratoin. He was right. I don’t dwell on my failures but build on my successes – it’s the only way.
So many of them that it needs pages and pages but the lesson is that always you learn from these problems and even if you cannot solve them surely someone else could and you can learn from that someone!! This what research is all about learning, observing and applying and then going through the cycle again 😉