Luck mostly. My first "real" bike came with a Selle Italia Flite and it just fit. Over the years I kept buying them. Then a few years ago my team had a sponsorship deal with a Specialized shop. The Toupe that came on my Tarmac didn't work for me so I asked them for the Specialized saddle most like the old Flite, which is the Romin. Turns out the Romin is even more comfortable. It's a little finicky to set up, but once you're dialed in, it just disappears.