*got high and ended up making a long ass write-up, but this is how I saw it***
In the intro, he starts out by saying you can't do this job if you can't deal with boredom. We then see his entire, long, tedious process of getting ready for the kill...all the monotony. It's like you have to be a machine to do the job. He also mentioned being 100% successful on every kill except for a guy who dropped dead of a heart attack that he couldn't claim. The botched kill we see is the 1st one if we believe him- so it's not as much about general incompetency as much as slipping.
We'd seen him get distracted a few, him complaining to his handler about nothing happening/no target. Him talking about how the distance kills are the least fun and least creative. He's mastered his craft and is bored. Starting to look more human than machine.
And he was getting distracted by the dominatrix thing during the botched kill. All the while, the song with the line "I am human and I want to be loved" plays in the background. At the end of the day, the Killer is still just a guy.
And the chain of events after the botched kill sets off him having to get up close and personal on every kill after in the movie. It culminates with the brute kill...that is the sloppiest kill possible, but also the one where he had to improvise the most.
The interaction with the Hodges handler makes it clear that the expectation is that the guy is a clean, methodical killer who operates more as machine than human too. Hodges doesn't think he's in danger at all until the last possible moment because he expects the Killer to do the rational, clean thing. Which he doesn't. He kills him with that nail gun.
And the Tilde kill reveals that he's not incapable of operating at a high level as much as just wanting to mix it up and play with odds more than certainties. He doesn't take the food because it's already out there when he arrives and he never sees her eat it. He grabs her drink to drink the alcohol that could be spiked because he doesn't think she'd kill him AND herself. He accurately guesses her knack for self-preservation, and is ready when she tries to pull that fast one on him and stab him at the end.
The Tilde convo is also the most revealing one too, imo. She's caught slipping at dinner, 1st of all, so caught relaxing and enjoying herself. She mentions thinking this day would never come, but clearly she got caught slipping and that was some arrogance. Then she talks about the Bear in the woods and the Sodomy...punchline being, "You know. I don't think you're here for the hunt." Hinting at subconscious motivations.
Maybe I missed it, but the one thing that would kind of solidify my understanding of the Killer's motives and what led to everything playing out...is if he was fairly recently with his girl. Just starting to enjoy a taste of the good life and enjoy the fruits of his labor.
His character was like the bizarro world version of the Sheriff from No Country for Old Men. Two characters recognizing when it's time to bow out of the game.
