I agree with the OP that looks are a big factor (nature's law), but the number of times I've seen a fit bird with a guy who is quite ugly (at best distinctly average) and thought to myself "how the fuck did he get her?!" runs into the hundreds if not thousands. The majority of these guys didn't pull them on a night out, most of them will have either worked with them and wormed their way in over time, or met them through a mutual friend (so there was never any cold approaching involved).