It's only a "Success" in the sense that it's still around at the end of the day. If its dead then it can hardly claim the title of "champion". The value judgment of "Good" or "Bad" , "Success" or "Failure" , "Winner" or "Loser" is very much related to "Living" or "Dead" because the dead ones don't get to play anymore. The winners get to keep playing. The dead ones are just that, dead. It's not us who imposed this rule, the very nature of life imposed this rule on us!
That explains why the organism is still around - our theory fits the observation. it still does not explain what the organism gains by reproducing, and the gain of an advantage in the environment is the key to adaptation.