Stress
The stress of this job can be overwhelming, especially when performing undercover work. Agents must act like criminals in order to build cases against actual criminals. Agents can face a number of psychological problems, including anxiety, loneliness, and isolation. Stress mounts if agents feel like the sacrifices they made by going undercover didn't result in enough convictions. It helps to avoid setting the bar too high. Not everyone can be Chuck Norris.
Not every ATF agent goes undercover, though. Agents perform other activities such as making arrests, conducting surveillance, interviewing suspects, obtaining search warrants, looking for physical evidence, participating in raids, preparing case reports, and brushing their teeth. Well, the "brushing your teeth" thing is just about everybody, but still...they do like to practice good hygiene.
Some ATF agents may find themselves working something close to a regular nine-to-five shift for most of their careers, but it depends on their skills, what part of the job they choose to pursue, and how the ATF needs to use them. If the agency decides an agent could be of best use as a hall monitor, ensuring that no one puts their mouth directly on the drinking fountain nozzle, it could relegate him to that duty. He'd have the option to quit, of course, but it actually sounds like a fun gig.