You've heard of good cops and bad cops. Well, Jakob and his canine partner Ellie are good cop and sad cop. Ellie's the good one, obviously. Jakob, of course, isn't not good. He's just really, really sad.
Jakob is a different kind of owner for Ellie. Ellie has had two previous owners in her earlier lives. As Toby, there was Senora, a woman with more dogs than she could handle. As Bailey, there was Ethan, the dog's favorite boy, who showered the dog with love and affection.
Reborn as Ellie, the dog has Jakob, a man who has torn out the dictionary pages for "love" and "affection" so that they're no longer in his vocabulary. The man has a one-track mind, and he is riding the workaholic express in circles. Ellie realizes this early on, thinking, "That is what we did together, that was our work, and that's what he cared about most" (19.25).
Jakob is a walking Rihanna song—the one with lyrics made up only of the word "work." As a result, he pushes Ellie to be the best dog on the K-9 force. Now, he never mistreats her. He cares for her, feeds her, and supports her—but he doesn't give her the affection she received from Ethan.
We eventually learn that Jakob has never got over the death of his wife. Workaholism is his way of getting his mind off her. Eventually, he has to give that up, because on a mission to rescue a kidnapped young girl, the girl's kidnapper shoots Jakob. He's okay, but the injury takes him off the force, much like Ethan's injury took him off the football team.
Here, Jakob and Ethan diverge. Ethan wallows in his own misfortune and ends up a bitter, lonely old man. But when we last see Jakob, he has a wife and a child. He has rebuilt his family. As Ellie observes, "[T]he coldness in him seemed to have gone away" (24.24).
Having time off work led Jakob to some introspection, and it served him well. We guess getting shot softens a guy up.