Why Do Saiyans Win?-

So your wondering how the saiyans in the Dragonball -Z-GT series almost always win?, how did they gain so much strength. To answer this question one must look at the situation they are in. Imagine someday, us human beings become the most powerful force in the galaxy. Taking over and ruling all other civilizations in our path. Well that is the kind of strength the saiyans had over their galaxy. Now imagine for some reason we were all caught off guard by something or someone that suddenly destroyed our home planet and %99 of our race with it. How would you feel? how would you act? Imagine growing up always with the thoughts in the back of your head; "i am the last of my race, i am the last hope for my ancestors and the future, I am the only one to represent my race". You would probably get your butt out of the computer chair your in right now and go do something constructive.!!!
Any way, that is the realization that the Saiyan's have a grasp on. Eventhough Goku has little association with the Saiyan race in general, he still always new that he was one of a kind, and different from everyone else on earth. Sure, the Saiyans have some abilities we don't. So what if they have enormous natural fighting strength, and some of them can fly at birth. Thats not the point. The point is, They carry enormous pride and passion in the knowledge that they are the last of their kind, they're the only descendents of the most powerful beings in the universe, and since Survival of the fittest is very true in their reality, they are the fittest.