No one ever asks John.
They don't want to know what he sees. They don't want to know what he thinks. They only ask his opinion when they already know he has the wrong answer and there's a point to be made from it. They—‘they' having expanded over the years to encompass not only Harry but also his adviser in med school, his commanding officers, Sherlock, Mycroft, various co-workers, some employees of Scotland Yard, and now from the looks of it Irene Adler wants in on the action—order him about, casually suborn his life, scathingly point out the large mathematical difference between their IQs and his when he gets so uppity as to try to weigh in on a conversation, and they sure as hell don't tell him anything.
By and large, John doesn't care. Hell, most of the time they're right, at least when it comes to the Holmes brothers. He seldom sees anything they don't. And John's self-esteem sure as hell doesn't depend on what other people think about him or, good god, Sherlock would've driven him to suicide by now. Which is a lesson he'd share with Molly if she'd only listen.
But sometimes... Just sometimes, cleverness trips over its own big feet, and John could show them a thing or two, if they'd let him.
And there's something they don't understand about John. His loyalties have shrunk. Oh, he still cares about preserving life, defending Queen and Country, all that. But mainly, these days, he cares about Sherlock. Because Sherlock is perfectly capable of looking after all the rest of it. John's job, as he sees it, is mainly to look after Sherlock.
He holds Irene's phone in his hand exactly once, the night she stays over with them. Sherlock's left it on the table in front of John, to keep it clear of light fingers while the great minds are off flirting in the kitchen. He turns it over in his hands, absently, while he watches them through the half-open doors.
Sherlock is standing at the stove, frying something in a pan. Irene leans provocatively past him, letting her loose hair brush down over his arm where he's got his sleeves rolled up. John sees her lips move, then his. They both grin.
John knows that smile, though he doubts Sherlock would recognize it in a mirror. Oh yes, John knows exactly what he's seeing. He’s felt the real thing, after all; he can’t be taken in by a fake.
John looks down at the phone in his hand and taps in a code. When it chimes gently, he looks at it for a moment and then hits the button to lock it again.
Sometimes geniuses keep the wrong things to themselves. Sometimes they miss what's in front of them. If Sherlock can't spot his own wandering heart, then John will look after it for him. The way he sees it, that's what he's for.
If they'd only ask John.