Jim is being an asshole for a reason. I swear.
Jim was born with a genetic advantage that causes his senses to kick into overdrive - sight, smell, hearing, taste, and tactile response. For example, he can see detail at night three hundred yards away with no difficulty, or tell the difference between plastic and wood after it has been burned in a three thousand degree fire. He's what Sir Richard Burton called in his 1885 monograph describing tribal watchmen and sentries who develop hyperactive senses from time spent in isolation, a "Sentinel".
Hence, the show being called 'The Sentinel'.
Jim's abilities can and do go wonky, if he's sick or if he eats something he shouldn't or any number of reasons. They also come with a zone-out factor: if he concentrates on one sense too hard, he loses all others. Which can be dangerous because he may not see or hear something coming at him. That's where Guides come in. Guides help and, well, guide Sentinels.
Say hello to the people, Blair.
Now, the reason this hasn't come up yet and why Jim's being an asshole. Jim repressed his own memories of his childhood when his abilities were active, and they became dormant. In the series, they become active again when his unit crashes in the jungles of Peru and he spends eight months with the Chopec tribe, although mostly alone. And then active again when he goes on a four-day police stakeout.
Jim is currently camping, alone, in the Preserve. Helloooo, Sentinel abilities. This is going to be fun.