This works fine and dandy in the first movie as he has yet to be born. It's not till Terminator 2 that we meet him in boyhood, played by Edward Furlong, who is mouthy, streetwise and a bit of a computer whizkid. He's also not short of a few guts. What happened to him after this? By Terminator 3 his mother is dead and he's turned into a whining looser. Even in the TV series he's constantly bemoaning what fate has in store for him and doesn't show much of the grit he'll need to become the leader mankind needs to destroy the machines.
In fact, if anything, the only person with real guts at all, time and again, is his mother, Sarah, who is the real hero of the franchise. It's a shame the filmmakers decided to kill her off with leukemia by the third installment. Indeed, one of the strengths of the TV series was that her death was sideslipped and she lived on.
So, what happened with John Connor? Did the filmmakers find it too difficult to turn him into the hero he was supposedly destined to be? Something definitely went wrong, because what we eventually got wasn't worth all the death and destruction of the first movie. They might as well have said to Sarah: train up and get ready. You're it.