Here's a good example, which led to my current relationship and son being born.

In 2009, I joined Facebook. I entered nothing besides my name, and let the account sit dormant for 2 weeks.

When I logged back in after those 2 weeks, I was shocked to see a friend suggestion of a girl I went to college with (and remained in contact with).

How could it know? I only entered my name. Even if it figured out which school I went to somehow, what led it to believe that I knew her?

It turned out that Facebook tricked her into uploading her e-mail contacts (with some very innocent explanation), and I was one of them.

So I added her as my first Facebook friend.

A short time later, it suggested another girl we both knew. This girl was on her friend's list. It is still not clear to me how it knew I knew this second girl, unless it was just picking randoms from her list to suggest to me (perhaps near her age?), and happened to select that one.

I added that girl, we started talking, and she ended up becoming Benjamin's mom.