If Sam had been the older brother, he would have been way wiser in the ways to help raise little Dean.
Take food, for example. Food as in everything other than what Dean spent a lifetime feeding him: poptarts and cheerios and too much coffee before he was even nine. No, really, too much coffee. He’s got the addiction to cafeine to show for it.
Given the chance, Sam would make sure Dean learned to eat and drink healthy. And no coffee before the age of sixteen at least.
Coffee’s not for kids, everybody knows it stunts your growth.
Sam would have rebelled. Oh yeah. He’d have put his fist down over a number of issues, he’d have told dad to shove it long before being done with highschool, he’d have applied himself to his homework and then applied for grants to all the good colleges around the country. He’d have gotten one, too, and he’d have gone for it, behind dad’s back even, up until the last minute when everything would have been settled and he’d have been ready to go.
So dad would have been mad, sure, and he would have told Sam to stay gone if he was so adamant to leave. But that wouldn’t have stopped Sam, oh no. He’d have rebelled strong and hard and all the way and gotten to wherever, Stanford or something, and he’d have gotten a couple of jobs to make up for what the grant couldn’t cover. He’d have been working hard at it and proving himself to whomever (not that dad would have cared, really) and he would have gone for pre-law and applied to law school, and he would have met someone probably, moved in with them, been happy... he’d have had the life John Winchester never gave his sons.
But most of all? He wouldn’t have gone alone.
Seriously, why are they still driving around in that stupid old car? Why? Because dude, talk about a bottomless pit. The amount of gaz that car burns for each mile... ridiculous. Now that’s something Sam would have done differently. Sure, it’s a pretty car, they’ve got history together, etc. But, not practical. Not practical at all. Not to mention the two important words: cassette tapes.
Now if Sam had been the older brother, he’d have inherited the car instead of Dean. And if that had happened? He’d have sold it for a good price and gotten something a little bit more sensible. Like Dad’s truck for example. Or maybe not a truck but some other car, something that doesn’t belong in a museum, something he doesn’t have to worry about when they’re chasing a werewolf down backway trails. Something with a CD player instead of that antiquated radio.
And anyway, what’s with Dean’s obsession with the thing? And be careful of the paint, and don’t slam the door too hard, and no eating or drinking inside because of the seats, yadayadayada. You’d think the car was more precious to him than anything else. It’s just a car for Pete’s sake, a little scratch doesn’t...
Wait. What the... what’s that on the door? Is that... That is! Oh, bloody hell. That’s a SCRATCH! ON THE FREAKING PAINT! MOTHERFUCKING WEREWOLF WAIT TILL I CATCH YOU YOU FUCKER! YOU ARE SO DEAD!
Choose hunting. Choose guns. Choose knives. Choose gutting demons and spending time with Jose. Choose meaningless encounters. Choose a fucking big car, with a fucking big trunk and a complete collection of classic rock. Choose cassette tapes and hustling pool........ Choose bad health, high cholesterol and no dental insurance. Choose credit card scams. Choose a life of motel rooms. Choose yourself over your friends. Choose hangovers and wondering who the fuck you are on sunday mornings. Choose hunting a demon you’ve never even seen , spirit-crushing nightmares, stuffing junk food into your mouth. Choose losing a limb, and eye, your life in the claws of a devil. Choose no future. Choose the family business. But why would Sam want to do a thing like that?
In Dean’s place? Sam would have chosen not to choose that life. He’d have made the choice for the both of them, he’d have chosen not to choose that life: he’d have chosen something else. And the reasons? There are many reasons.
But who needs reasons when you've got common sense?
If Sam had been in Dean’s shoes that night, if Sam had been the older one, the one holding baby Dean in his arms as the flames devoured the house and their mother... he wouldn’t have stopped running. He’d have taken his baby brother and he would have run, and run, and kept on running until everything was different.