There’s a certain spike of interest (also known as dopamine) in novel experiences. If you love your new job, but never gain new responsibilities and instead practice the same motions day in and day out, you’re most likely going to get sick of that job you thought was the best thing since sliced bread.
(On an unrelated note… why is sliced bread so great?? I actually love having a loaf of bread and just breaking off chunks or slicing it myself. *Shrug*)

This can be compared to the case...