 When I was working on my thesis on rocket propulsion, at that time I was taking a course from Fritz Zwicky on analytical mechanics. And one day after a lecture, I went to him and I said, I'm working on this problem and I'm a bit puzzled about something. And well, he was in that kind of a mood that day. And so he sort of shouted at me and told me I was a bloody fool, that I was trying to do something that was impossible because rockets couldn't work in space.