1. I’m tired of this job. I do the same old thing day in and day out. I’m in a rut.
2. Don’t let yourself get into a rut. Try something new from time to time, and you won’t get bored.

Synonym: on a treadmill. Compare to: old hat. A rut is a groove or narrow track pressed into a dirt road that catches the wheel of a vehicle and forces the vehicle to go in a restricted path that the driver is unable to alter. The expression connotes going in a direction or doing an activity without being able to vary it.