He really does love his job.
The thought that he's getting paid to look at someone who, in most cases, deserved to still be living their life just like him did get to him for a while at the start, but over the years he's had to try his best to compartmentalise that part of him. He knows full well now that he can't do anything to change the circumstances by which someone comes in to his table, but that alone provides him with enough reason to contribute towards stopping something like it happening.
The buzz of getting a new case giving him a fresh puzzle to solve piece by piece is incomparable to anything else. He knows how to take that body in front of him apart and figure out what made it tick – and what suddenly caused it to stop doing so – then show the detectives what he's found afterwards. And he adores it.
Sometimes, a case opens him up to a whole new world of research and that to him is the best thing about his line of work. There's nothing he likes more than burying himself in books and articles and prodding and probing into something he's never come across before, and it's always so damn useful sharing it with someone else when he's reporting back his findings.
What he doesn't know, however, is just how admirable everyone else finds that spark of passion that so brightly ignites when he's working on a case with them.