The days I am brewing are the days I am happiest. All the CIP, transferring, carbonating, keg-filling, sample-glass washing, scheduling, opening/closing, growler filling, etc. are all the things that wear me down.
Nothing compares to the feeling of eyeing that hydrometer and making a note of the starting gravity before I pitch some yeast. Serious anticipation, pride, and a feeling of a job well done. Then coming in 8 hours later to a serious gurgle in the air-lock bucket is just icing on the cake.