‘Chance favours the prepared mind’ implies both an element of luck and a prior understanding of what is normal. Making successful discoveries in astronomy is not comparable to buying a lottery ticket and then sitting back but requires a deep familiarity with the Sky, the Universe, cosmic phenomena and/or physics. It does require both sides; you don’t make discoveries without making observations and you don’t identify them as such without knowing when something is new.
This, of course, echoes what I've written earlier in one of my entries on "Imagination Without Knowledge Is Ignorance Waiting To Happen".
However, to know what is new and unexplained, one has to first make sure one knows what is known and understood! Without that, one would not know what is new even if it comes up and bites on one's rear end.
Crackpots, especially, can't stand the thought of that! :)