It’s a definite misconception between Stan and the Winchesters!
He doesn’t quite see himself the way they want him to…
It took seconds for Stan to grab the clip near the top of the pen and haul it all the way back to Sam, panting a little from the effort as he stepped back to give the human room to take it.
Sam was frozen in his search, not having expected Stan to suddenly shoot off in a different direction while they conversed. Seeing how much effort it took Stan to drag the pen over to him drove into Sam how different they were in size, making him feel obnoxiously oversized all over again.
Dean had an identical look on his face, not knowing how to react.
“S-Stan,” Sam managed to get out, delicately picking up the pen. He’d been looking for one, but– “You can just… tell me where the pen is, okay? You don’t have to go through all that work, I can just grab it.”
The ghost of a proud smile that had found its way to Stan’s features for finally making himself of use melted when he saw Sam’s reaction. Now he was confused all over again, worried that he’d done something wrong.
“But… you wanted it…” Stan trailed off awkwardly, trying to think of a way to fix it. But there was nothing to fix. The pen was fetched, Sam already had it. He didn’t understand why the brothers seemed so averse to his actions, but he resolved to do better next time as soon as he found out.
“That’s… not what I’m saying…” Sam said, his conviction fading at Stan’s reaction. “Just… If I want something, you don’t have to get it for me.” It was so hard to come up with words for what he meant. “I don’t want you straining yourself.”
“You’re not a pet,” Dean interrupted, putting it far blunter than Sam would have done. “You know that… right?”