Like the film noir detectives that came before him, Jake exhibits some of the common traits of a hard-boiled private investigator. He appreciates crass jokes, shows a willingness to get violent with both men and women who cause him trouble, and never lets physical threats scare him off a case. Unlike the traditional private eye, however, Jake can be disarmingly human. Though he isn’t scared by physical threats, he is susceptible to them and spends a good portion of the film wearing a large nose bandage. He starts the movie reluctant to take on a job he feels won’t satisfy a client. Unlike most Hollywood private eyes, Jake tends to be wrong more often than he is right, missing important information and putting clues together incorrectly.
The element that brings depth to Jake’s character is his odd inability to comprehend the larger picture. Nicholson subtly weaves in this shortcoming as his character develops, mainly through tantalizingly vague references to Chinatown, where the corrupt stay corrupt and everyone is supposed to look away. Jake was never very good at looking away, no matter how much trouble it caused him. Sadly, this also tends to cause trouble for other people, especially Evelyn Mulwray. Jake is a man perpetually in over his head.