Only reason we knew was the D.A.R. (the man in question was a Revolutionary Ancestor.)
On the other hand, when my dad was a young schoolboy in Rome, GA, he was sitting on the levee below Darlington School with five or six classmates.
They got to talking and realized they were ALL cousins. Of course, this was back when Rome GA was a whole lot smaller than it is now.
BUT, on still another hand, when I was doing some family research in Rome, somebody referred me to a local physician who is an amateur genealogist and unofficial historian of Rome . . . and it turned out we were cousins, related through one of my great-great-grandmother's brothers . . .
amazing isn't it?