This stanza closes the episode “Something Wicked”. The two last lines seem to fit Sam, but for the purposes of this episode, the first two lines fit Dean. This is the flashback episode, the only one besides the pilot that shows anything from the past. It's told from Dean's POV, which gives it his slant, but one I'll take as "true" for this meta. Dean's pain, his need to protect Sam, his belief at failure in his charge, all seem to stem from the one incident in Fort Douglas, Wisconsin. We don't learn the exact date, though Sam does say Strigas only appear every 15-20 years (via his research).
I believe fans set Dean at age ten Dean is nine in this flashback, though I would put him on the cusp of 11, just for maturity. (I wouldn't label Sam as older than 6-7 anyway)
So, we have a nine year old boy, charged with watching his little brother, and from the vocal "eye roll" Dean gives his father, this is nothing new. (holding gripe about Papa because I didn't draw him for this meta *g*). We can assume that nothing "bad" ever happened when Papa was away, because Dean didn't look guilty when he leaves. A nine year old boy who is capable of firing a gun and is taught to "shoot first, ask questions later", yet leaves his younger brother alone, obviously doesn't see the "need" for all Papa's fuss. This is the third night that John's gone, and that doesn't appear to worry Dean either. (really, really restraining from Papa-bashing). Also, Dean at nine is able to use a hot plate, presumably smart enough to not let strangers in, and is capable of taking care of another human being (as much as a younger sibling can be "human"- I have one of my own *g*).
He seems like a fairly normal kid, annoyed at his kid brother and whining about not getting the last of the Lucky Charms. Then he does another normal kid thing - goes off and plays video games.
The normalcy is shattered when he returns, and the Thing is hovering over his baby brother. Has Dean seen a monster before? Was he scared for Sammy, or scared that he would have to shoot the gun? Was he scared he might hit Sammy? All this on a nine year old boy, and John blames him for leaving Sammy. Yes, Dean disobeyed orders, but what nine year old wouldn't? Per the pilot, when Sam was nine, he told John he was scared of the thing in his closet, and John gave him a .45. It appears that Sam and Dean learned the monsters were "real" around the same time, but I get the strong impression that for Dean, it was a much more traumatic experience.
If we take Dean's "Dad looked at me different," after that [incident] at face value, then Dean lay a heap of guilt at his own feet and it became part of his inherent nature. Because men are men and don't talk about their feelings, Dean bottled everything up inside, going so far as to not want to tell Sam in present day what happened back then. Dean doesn't help research the Striga, only correcting whatever info Sam digs up.
We've seen Dean interact with kids before ("Dead in the Water"), and his speech and behavior toward Michael just blows me away. He talks to kids on their level, not condescending or babyish. I dare say he *understands* kids, even if he can't name three that he knows. Well, at this episode he can, with Jenny's kids in "Home", Lucas in "Dead in the Water", and Michael in "Something Wicked". He treats Michael with respect, explains why he and Sam need Michael's help, and explains the dangers. It amazed me that Dean took the time to explain how a gunshot would sound, and that it wouldn't be like the movies. He made sure that Michael understood he was under no obligation to help them, yet his calm assurance probably helped sway Michael into trusting him.
One thing Dean said to both Lucas and Michael: "It's not your fault". Yet Dean fully blames himself for nearly getting Sammy killed. Shifting a bit to Sam here, in the earlier episodes, Sam seems to uncover a lot of previously unknown information via Dean. Dad was proud of Sam. Dad talked about Sam all the time. Dad swung by Stanford to make sure Sam was all right. Dean tries to be strong for Mary every day. Dean swore he would never go home again. Dean's afraid of flying. In Something Wicked, Sam learns why Dean always follows dad's orders: the one time he didn't, Sam nearly died. After the fight in "Scarecrow" about Dean always doing what dad says, this really packed a punch.
"I'd give anything not to tell you this." Dean's words to Michael, and the pained anguish on his face shows me he truly means that. He doesn't want to tell Michael the monsters are real; he doesn't want to use Michael that way, but he won't let the Striga live. This is Dean's vengeance. If John and Sam can have theirs toward the Demon, then Dean can have this. Blasting the Striga in the face way more than necessary - to ensure it was dead of course - and the look of satisfaction on Dean's face, said it all, really.
As the brothers watch Michael and Joanna drive away, Sam wishes he had that kind of innocence. Dean wishes it for Sam as well, but doesn't say he wants it for himself. That's been a telling line for fans, and it's one that gets to the heart of Dean. The encounter with the Striga, facing a monster for himself, woke Dean up to the things out there. He lost what innocence he had left (and it looked like quite a bit, judging from his actions pre-Striga in the flashback), but incorporating that into his core personality, he chose to save people and hunt things, in that order. Even before they encountered the Striga, that's been Dean.
Dean has a reason for everything he does; he just chooses to keep some of those reasons to himself.
I honestly wanted to just say "Woobie!Dean" and call it a done meta, but common sense (and the threat of no more goodies from deannie) have forced me to try to come up with something for Dean.