Luck, chance, serendipity. A. C. Fabian in "Serendipity in Astronomy" has offered his opinion...
Astronomy is an observationally-led subject where chance discoveries play an important role. A whole range of such discoveries is continually made, from the trivial to the highly significant. What is generally needed is for luck to strike someone who is prepared, in the sense that they appreciate that something novel has been seen. “Chance favours the prepared mind” in the words of Pasteur (1854).
This is one definition of serendipitous discovery, first identified as such by Horace Walpole in a letter in 1754 to Horace Mann on discussing a Persian tale of three Princes of Serendip. We shall hear Several more interpretations1 are outlined in these chapters, but I shall stick with the concept of a chance or unplanned discovery. In contrast with school laboratory science where the aim is to plan and carry out an experiment in controlled conditions, in general astronomers cannot do this and must rely on finding something or a situation which suits. Often, the possibilities afforded by a phenomenon are only appreciated later, after the surprise of the discovery has worn off.
"Serendipity in Astronomy"