Not as in Serendipity, which is a famous fly, but as in serendipitous, like when a bunch of things come together to cause a particular result. Without listing all the things that converged to make these flies emerge, suffice it so say that it was an unusual set of circumstances that resulted in this fly coming off the vice.
The fly was tied for a very early PMD hatch on my home water in Northern Idaho. Early as in mid-April. And it has been a hatch that produced very large PMDs that hatched somewhat later in the day than the PMDs that I am accustomed to.