I was thinking
One day, I got a piece of paper and tried to figure out how long I spent on my PhD. This was because of the oft-repeated idea of the 10,000 hour rule that people attribute to Malcolm Gladwell, i.e., to truly become an expert you have to spend 10,000 hours of practice at it. Having completed a PhD, was I now an expert? If I could figure out how many hours I spent on the PhD, then perhaps I would have an answer!
I wasn’t being entirely serious, but it was interesting to me. So I got a piece of paper and started doing maths.