Ove never understood why Sonja chose him. She liked abstract things, while Ove liked things he could hold. She always told him that she knew he was dancing on the inside, which he resented because he thought dancing was haphazard. Ove wanted things to be right or wrong, not muddy.
Sonja is an interesting figure as Ove's love interest because he does feel so strongly that people who don't do things are less-than. This suggests that Ove's love for Sonja was stronger than his principles and beliefs, and helped shake up the rules he usually adhered to.
The night after the house fire, Ove slept in his car. Two days later, two men in white shirts showed up. They told him that they'd been sending him letters and explained that Ove had no choice but to sell them the land where his house stood. Ove studied the forms and realized he hated the men in white shirts. He signed the document and rented a room from an old lady in town.
Again, the white shirts are doing things that don't help people, and Ove has no power to resist them. This marks the true beginning of Ove's hatred for men in white shirts, and he hates them primarily because their rules don't have goals that do anyone any good (at least that Ove can see).
The next morning, Ove passed Tom in the hallway at work. Tom loudly called Ove a thief. Ove ignored him, went into the changing room, took off his clothes and his father's watch, and took a long shower. When Ove came out of the shower, his watch was gone. The narrator says that it was like someone removed a fuse in Ove's mind. Naked, Ove walked into the foremen's changing room, grabbed Tom, and yelled for him to return his watch. When Tom insisted he didn't have it, Ove dug in Tom's coat pocket, found it, and punched Tom. Later in the hospital, Tom insisted he'd slipped, and the other men in the changing room claimed to not remember what happened. Ove decided that was the last time he was going to let someone trick him.
When Ove snaps, he stops acting generously and thinking charitable thoughts about people. He decides that getting his way and making sure that the right thing is done is more important than being kind and generous, particularly where people like Tom are concerned. Ove insists that his belief in fairness needs to also include himself and how people interact with him. This shift in demeanor explains why in the present, Ove always thinks that people are looking out for themselves. Everyone he's met thus far is doing just that.
Ove quit his job at the construction site. His coworkers gifted him a toolbox with new tools to "build something that lasts." Later in the year, Ove enlisted in the military and scored well on all the tests. The military appealed to Ove because of the uniforms and order. Ove's happiness was shattered quickly when he failed his medical examination. Something was wrong with his heart. The white-shirted army man told Ove that rules are rules.
Not everyone is bad: the construction workers give Ove the ability to build things and remember the community he had at the construction site. The military also appeals to Ove's love of rules, regulations, and principles, but the military follows rules that prioritize the organization over the wishes of people who'd like to serve it.
When Ove returned to his night cleaning job on the railway, he got quieter and quieter. Ove's landlady found him a garage in which he could work on his Saab, and Ove took the car apart and reassembled it. When he was done, he sold it and bought a newer Saab, which he promptly took apart and reassembled. His days passed slowly and peacefully until he met Sonja.
As Ove gets quieter, he does more things like messing with his car, which very much connects him to his father. The landlady is kind to Ove and seems to care about his happiness, which complicates Ove's belief that all people are out to get him.