1 Work in Argus Filch & Irma Pince
Argus' life was a largely thankless one (unless you counted the thanks of the paintings he maintained), working on keeping a thousand year old castle from falling down around the ears of students who didn't care. He had his cat, his work, his books, and a constant boil of self hatred and resentment to get him by.
And then a sixth year handed him a letter from her aunt, thanking him for acting as conservator of Hogwarts and calling him Dr. Filch. It was the first time he had been called Doctor since he started at the castle. He had little choice but to write back, after that.