Isn't this one of life's great fallacies?
My best friend has been having lots of rampant sex on a fairly regular basis for a couple of months now with a girl he was friends with for two years, giving each other lifts to work and generally not looking at each other
in that way, but then one night they were alone together and it just happened. I myself hooked up with and had a long-term relationship with a girl I'd been friends with for
six years. During friendship you learn a lot about each other, and a solid friendship can make a solid foundation for a relationship since a lot of the qualities that make a good friend also make a good partner. If you're physically attracted to each other I wouldn't say being friends necessarily means going further is off the cards ; you just judge each case on its merits and decide if the friendship is worth taking the risk. And it usually is, if it transpires you're ready to give it a serious go.
Hell..... Chandler & Monica.