Some people thrive in jobs where they have discrete projects, ones that have a set beginning and end. This includes teachers, where each semester is time-bound. And contractors, architects, police detectives, etc. They all operate with discrete tasks that last between weeks and months.
Others prefer continuous improvement jobs, where the job includes perpetual rolling tasks towards an infinite end-goal, often doing the same thing day after day. This includes athletes, who set interim goals, but for whom training is ongoing. And business executives, and doctors.
I'm in a job of the latter variety, but in order to quench my need for discrete goals and tasks, I have to build artificial milestones for myself. Gives me concrete goals to look forward to achieving. The goals can't be too big (sell a company) or too small (see a patient), they need to fit into that weeks-to-months sweet spot.
Are you in a job that's congruent with your preference for discrete or ongoing tasks?