Acts 12:25 And Barnabas and Saul returned from Jerusalem, when they had fulfilled their ministry, and took with them John, whose surname was Mark.
Barnabas and Saul had gone to Jerusalem. They knew why they went and what they were supposed to accomplish. They were able to leave knowing that they had finished their work.
I think that maybe one of the problems we have is that we do not think through what we are supposed to accomplish where God sends us. We live without thought and plan. We never feel that we have fulfilled our work because we never thought through or prayed until we had in mind what God wanted to accomplish with us.
I know that much of what we do does not have a finish date but maybe from this we could get an idea and it might help us feel the thrill of having fulfilled the work. For example, share the gospel message clearly with my class. That is Biblical and it is doable. Witness to certain people or a certain number of people. Give out a certain number of tracts, etc.
The point is that we should know something about what we were sent to accomplish more than just spend or pass the time.