I also vividly remember the moment I had idea 1 from my list above. It was such a nice warm autumn day in the last months of a very turbulent year: I struggled

I also vividly remember the moment I had idea 1 from my list above. It was such a nice warm autumn day in the last months of a very turbulent year: I struggled finding something worth doing a PhD on, and in the 10 weeks before, I got married, my wife got pregnant, was rushed into emergency for a suspected ectopic pregnancy a few days later, which then suddenly turned out to be a completely normal pregnancy. I also had an upcoming conference talk a week later, for which I was completely unprepared. Suddenly the idea was there, and it was like a door to a wide avenue opened, with follow-up ideas left and right all along the way. It turned out quite beautiful in the end, and when we published 6 months later, one of the reviewers found the idea "elegant", which was by far the most positive thing I ever read in a paper review.