Oral hygiene is really important, especially if you are a building. Architects recommend brushing your windows twice a year. If you don’t brush, the accumulating debris will contribute to view decay and constant bad moods for your irritated residents.
A clear window allows you to see for smiles, and smiling helps you maintain a healthy mind.
For this reason, window cleaners should be recognised for original contribution to sanity and be rewarded honorary PhDs.
Trees, unlike buildings but very much like cats, clean themselves. Their smiles are always bright, and they don’t need PhDs because they’ve already written all the books in the world.