What is with the "I saw him first rule"?

I saw him first applies to first dibs if the first girl fails with out entering in to a relationship with him then girl one two and three have a chance. If the first girl fails after getting involved with the guy then he is off limits unless he is truly worth your friend ship or first girl says it is okay. If she thinks she has sole property over him forever because she saw him first she is sadly mistaken.