As he flipped through his brother's journal, Sam couldn't help but wonder how he'd underestimated his brother so badly for so long. In-depth histories, precise notes, photos, sketches and clippings all neatly arranged.
The daevas in Chicago, he remembered Dean asking for tape and then outlining the symbol on the floor. Looking back on it, Sam doesn't think he would have thought to play connect the dots with blood spatters on a rug. Dean did, he saw the pattern and unerringly followed it, bypassing splotches of blood that were irrelevant. He remembers phone call from Dean when he figured out what they were dealing with. With a flush of shame on his cheeks, he recalls asking Dean how he'd figured out what they were dealing with.
"Name the last book you read."
At the time he mistook Dean's slight pause for mentally grasping at straws, trying in vain to remember when he'd last read a book. Now he suspects it was Dean momentarily struggling with whether to tell him the truth or not. Dean had finally said he had called Caleb for help. Sam is willing to bet if he asked Caleb about it he would find that Dean never contacted the other hunter.
"...go back to school and be a person again." As if his brother isn't a person because he doesn't have a "normal" life.
"I don't want you to leave the second this thing's over, Sam."
Anger and hurt flared in his gut - why had Dean been playing dumb for so long when he obviously was anything but? Why hadn't he just leveled with Sam, helped with the research, taken his fair share of library duty?
From one heartbeat to the next, all that anger turned inward. Because hadn't Dean been trying to show him all along? Didn't he call with the information about the daevas? Hadn't he made his own EMF meter from scratch with just what he had on hand? And what had it gotten him? Sam's stomach twisted when he remembered again his sneering condescension any time Dean had offered up anything Sam deemed "too smart" for his dumb older brother. His outright refusal to accept Dean could possibly have thought for himself. Why should Dean have to scream from the rooftops something Sam should have seen for himself if he'd only been looking?
When was the last time he actually looked at his brother? When had the hero worship turned into something so ugly?
"Dad let you go on a hunting trip by yourself?"
He took in the clear delineation between "pre-picking-Sammy-up-from-Stanford" and "post-picking-Sammy-up-from-Stanford" in Dean's journal, realized how much of the research and background work he had relinquished to Sam. He remembered those first awful weeks, consumed by guilt and exhausted beyond all measure. Grief and loss threatened to drown him, he clung to thoughts of revenge as if they could buoy him up above the pain. Thinking back on it with a clearer head, he could pick out with stunning accuracy the pattern his brother would clearly have seen immediately.
Any time Sam came close to toppling off the ledge of despair, Dean would nudge him into researching this or that. The current case, the next case, connections between cases, all of the things Dean had meticulously and painstakingly documented in his journal prior to that fateful weekend. His brother had relinquished at least partial control of one of the most important things in his life to try to help Sam hold it together. He just never took that control back after...well...after.
Even in the early days, before Sam got enough of a grip on himself to be useful at all in any capacity, Dean did a lot of the researching either splitting the duties or working alongside Sam in whatever dusty library they could find.
As he searched through Dean's journal looking for the info on the current case he knew was in there, despite the gravity of the situation he couldn't keep himself from wondering what else he never realized. He couldn't stop thinking about what other things he had been so wrong about when it came to Dean, couldn't figure out when he'd stopped seeing his brother as the best thing in his life and started seeing him as inferior.