@Luc Wyn If you read one or two pages from Chapter 1 of
press.princeton.edu/chapters/s7576.pdf you will get a feel for what Walpole had in mind when he coined the word. Serendipity began as incredible, unbelievable good fortune and has devolved to mere good luck. Fortuitous began as "by chance" and has become" having good fortune." Over time the meanings have converged.