Link is super smart. Like, really, ridiculously smart:
Link skipped third grade because he could already do long division and fractions in his head. He taught himself to read. I am not an idiot, but I am not the smart one in the family. (1.32)
Although we have no doubt Ellen is pretty smart, too, Link is the one who is known for his mega-brain. He's so smart, in fact, that he feels his prodigy status entitles him to be an irascible jerk most of the time. He can do high level math without breaking a sweat, he devours advanced novels like they're Cheetos, and he has a natural skill in language that most polyglots would die for:
Dr. Koch arranges for Link to take another exam. This one in French. The results confirm what they have guessed after conducting four of their sessions in French. With only three and a half years of high school French, Link has become fluent. (19.1)
Oh, and he's musically talented, too; he can play piano like it's nobody's business:
Link can play almost anything by ear. James plays the piano really well (Link says his technique is excellent), but he needs to have sheet music in front of him. James thinks his own piano lessons are boring, but he loves when Link plays. They listen to a lot of music together to see if Link will be able to play it after hearing it just once. (2.39)
And don't forget, as if all of those admirable skills weren't enough, he's athletic, to boot:
The next morning it is still raining. Link has gone running by the time I drag myself out of bed. He is on the track team at school and runs, rain or shine, seven miles every other day. James says that the running is the only part of my brother he cannot—will not—approve of. James has asthma, and his opinion of anything athletic is fairly low. He says running is a total waste of Link's time. I privately think it's kind of cool that Link has something he does no matter what. (2.26)
Sometimes, it seems like there isn't anything Link can't do. However, there is one pretty crucial flaw in his projection of perfection: The kid cannot communicate. Link suffers from what the doctors at Shmoop have diagnosed as "emotional constipation." His problem is twofold: (1) He is extremely conflicted about his sexual identity, which ain't easy, and (2) he refuses to talk to anyone about anything personal. Sure, he can debate the merits of John Woo films until he's red in the face, but ask him how he feels about something and he'll clam up faster than an initial suspect on Bones.
Why is talking to people so hard for Link? Well, it doesn't help that he's so smart. We're pretty sure he gets trapped in his own (substantial) brain and has no idea how to convey to other people what he's going through.
But it also doesn't help that his father puts so much pressure on him, either. Imagine having someone you love and admire constantly judging you, making sure that everything you do contributes positively toward building a perfect "mind's heartbeat" (2.16). That doesn't leave a lot of time for goofing around or just having fun. His dad only wants what's best for Link, but sometimes his ambition clouds what the "best" really is. That must feel pretty suffocating for Link.
Finally, Link has a hard time reaching out because his entire family is practically allergic to conflict:
My whole family's reaction to any kind of conflict is to avoid it. Each of us would prefer to spend money or chew off a limb rather than have a fight. Our aversion to fights is a quiet one except for Link. He always makes a big drama out of removing himself from an argument. The rest of us are more low-key about it. (1.27)
Link has been raised in such an emotionally sterile environment that he has no idea how to handle conflict, so he's navigating uncharted waters as he struggles with his own identity, particularly when it comes to James.
Link is a tortured genius, haunted by his superior intellect, ambition, and the expectations that have been placed on him because of these qualities. To make matters worse, Link's inability to communicate has left him isolated on his own little island of turmoil, leading him to feel like he's the only person ever to suffer from indecision and doubt.
This creates a lifetime's worth of suppressed adolescent hostility that gets released toward the end of the book. Unfortunately, though, Link is stuck expressing this anger in passive-aggressive ways, like turning in his exams blank. The only one who sees through this, bless her, is his Mom:
"There is nothing wrong with silence," Mom says, pouring her tea with one hand, holding her drink with the other. "It's not a bad way to express yourself. What concerns us about your silence is that you are not sure what you are expressing with it."
"I'm sure," Link says. "I know what I am expressing."
"I'm not convinced you do," Mom says. "It's a bit too loud for you to be so certain."
"What will it take for you to believe I know what my silence means?" Link asks.
"When it's not so hostile," Mom says. "I don't mind the hostility aimed at us, but so much of it is landing on you." (15.20-24)
Man, she has him nailed. Link is so angry because he's confused, and that's not a natural state for someone as smart as him. But that's one of the side effects to Emotional Constipation: If you repress your feelings for too long, you lose the ability to understand them.
Link has to do some real soul-searching before he will finally find his own happiness. At the end of the book he still has no idea whether he's gay or straight, or what his sexual orientation may mean for his future. On top of these huge issues, he's trying to navigate one of the most challenging periods in life: He's headed to college, where you're supposed to discover yourself and your life's calling. Add that to the confusion that's already fogging up his brain and you get one perplexed teenager. For Link, this translates to anger, and we really hope he eventually finds a way to figure himself out.
Lest we start thinking Link is a totally unredeemable character, he has moments of real sweetness, particularly toward his little sister. The night before her birthday he lets her sleep in his room like they used to do when they were little, despite not feeling particularly social:
He gets out of bed, and while he's whispering (instead of singing) "Happy Birthday," he clears a space on the floor, where he makes up a sleeping area with a quilt and two of his pillows.
"You take the bed," he says, the way he used to when I was nine. (1.60-61)
That's downright adorable. And it isn't a one-off; there are other little moments when Link allows his affection for Ellen to shine through, too. For example:
Sometimes, when he is at a piano, Link will play a song for me. Dumb songs that I love from The Sound of Music and Camelot. I never request anything, of course. (2.40)
Even when they're in the midst of an awkward silent fight, Link allows Ellen to come on runs with him, which seems like a giant concession for someone who really values his alone time:
The running is a lot like an old memory, even though I have never done it before. When we finish, Link says I can come with him again whenever I want. I am, it would seem, forgiven. Up to a point. There are definitely things he does not wish to discuss with me […]. (8.3)
Ellen has, over time, become an expert at interpreting Link's unspoken ways of displaying affection—which are really his only displays of affection. But hey, beggars can't be choosers, right?