It sounds like this is a writing experience your teacher has assigned to you. In order to get you started, I have a few ideas for you, although I can't write the piece for you.
- Think about the work towards a goal: performing a piece with an instrument, playing in a competitive sporting event, or even giving a dramatic performance. We have to go through significant amounts of practice whether it is memorizing lines, building muscle memory or making our fingers work the instrument. But the satisfaction of pleasing an audience are tremendous.
- Another possibility is just working out. If you don't exercise for quite some time, getting started again is terribly difficult. It's hard painful work. But the pleasure of breathing comfortably and having the strength to do things you don't always do is nice.
- School sometimes stinks. Walking across the stage for a graduation is quite fulfilling.
Hope these idea starters help!