Disclaimer: The Petrellis and the rest of the Heroes cast belong to Tim Kring; characters and concepts borrowed for fun, not profit.
Spoilers: Set pre-series; spoilers for the first two episodes.
Nathan Petrelli has always prided himself on being rational.
It's an important quality. The world isn't kind to dreamers. Start reaching for the stars, and you're only ever going to be unhappy that you didn't get to grab them. You need solid, sensible goals and a roadmap to achieve them. That's the route to happiness, or at the least contentment.
And there, right there, he can practically hear Peter bursting to interrupt. Peter would say contentment isn't good enough. That anything short of the mythical perfect isn't good enough.
Peter's never learned to fear what happens when you shoot the moon and miss.
They shielded him too much, Nathan thinks now. (Though he knows deep down that he'd do it again, a thousand times if he could.) It was always Nathan's job to get him away when Dad had one of his 'little episodes'. Take him to the park, take him out for ice-cream, keep him away from the house until blood and vomit and panic could all be safely papered over with clean white bandages and lies.
Peter never saw, so Peter doesn't know. He lives in a world with no consequences, where the curtain comes down between scenes and other people rush in to clean the floor and straighten out the furniture. He's never witnessed what can happen when you let your grip on rationality slide.
If their father was rational, he would have been happy. He had success. A wife. Two sons. A good life. A good reputation. There's no motivation for suicide in that. There's no reason.
Nathan doesn't know his father's reasons, and he doesn't look for them.
He's always been scared that the seed of it is in him somewhere, and if he tries too hard to understand he might succeed more than he wants to.
That's why he's never told anyone about the dreams.
Dreams of falling are one of the most common nightmares. He read that somewhere, and if it's widely believed true, then it's the truth.
He's never been able to make Peter understand that. That there's no such thing as an absolute truth, only what people perceive as truth. It doesn't matter if the sky turns purple tomorrow; everybody knows the sky is blue. It's pretty much immaterial what the sky actually looks like. People know what they expect, and the world had better give it to them. Their minds don't change just because the world does.
Dreaming of falling is a nightmare. Accepted wisdom, therefore fact.
But Nathan's dreams aren't nightmares. And he's not falling, exactly. More... floating. He steps off the edge, but he doesn't fall. Or he does fall, but he knows he could stop it if he wanted to. There's never a crash at the end, and he always wakes up feeling happy. Relaxed.
They're not nightmares, but that doesn't mean that they don't terrify him.
It's all right to dream of irrational things when you're asleep. Kind of the point, in fact. It's just that sometimes...
Sometimes, the floating feeling doesn't leave when he wakes up. It follows him around for the rest of the day, an extra bounce to his step, a little voice at the back of his head that whispers he could be immune to gravity if he would only push...
Sometimes it follows him onto the tops of high buildings, and it says, jump.
He wonders if his father ever heard a little voice like that. If it said to take the pills, it's okay, they won't hurt you, you can float. Do what you want. You're immune to the law of gravity.
Nathan knows he's never been the best at resisting temptation. But that's because he's always been good at analysing it. It's hard to guilt yourself out of doing something when you've already worked out all the angles and risk-to-reward scenarios. He follows temptation because he's safely assured of where it leads.
But the voice in the back of his head doesn't even sound like temptation. It doesn't feel like a wild flight of fantasy. It's the same voice that says: don't forget to call Mom. Pick up a newspaper on your way home. Wear your blue jacket, it's raining. Jump off the edge, you can fly.
These days Nathan avoids high places as much as he can. He takes the elevator, never the stairs. And he doesn't linger too long at windows.
He's not going to jump. He has no reason to. It's not rational. He's not going to kick off from the ground and try to fly.
Even though he's sure that he can.