A Serendipity

1. An unsought, unintended, and/or unexpected, but fortunate, discovery and/or learning experience that happens by accident. Serendipity - Wikipedia

Synonyms: chance, luck

2. A combination of events which are not individually beneficial, but occurring together to produce a good or wonderful outcome.

Antonyms: Murphy's law, perfect storm

Serendipity is sometimes used loosely as a synonym for luck; more careful usage, particularly in science, emphasizes specifically "finding something when looking for something else, thanks to an observant mind".

The term was virtually unknown until the 1870s, and gained currency in the early 20th century. It became popularized at mid-century, and is now widely used.[1]