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One would use the word 'serendipity' to characterize something that happened out of the blue, without a prior expectation for it to happen. For example, a person finding a $100 dollar bill on the floor of a public corner would be serendipitous.
Assuming this definition of 'serendipity', which certainly has a positive connotation, what are some antonyms? For example, the word (antonym here) would describe a person working hard for a full day to earn a $100 dollar bill.