Right after the scene where Goose hits the jettisoned aircraft canopy head-first and is killed, Maverick is shown washing his face and Viper meets him:
Viper: You fly jets long enough, something like this happens.
Maverick: He was my RIO, my responsibility.
Viper: In my squadron in Vietnam, we lost eight of 18 aircraft. Ten men. First one dies, you die too. But there will be others. You can count on it.
What's the meaning of "First one dies, you die too" mean?