A woman named Linda Blair . . . not the girl from "The Exorcist", a different Linda Blair . . . is a clinical psychologist in England. And she says that listening to Christmas music too early in the season is bad for your mental health.
Why? Because it's a reminder of all of the STRESSFUL stuff you have to do to get ready for the holidays.
In other words, when you hear "Holly Jolly Christmas", it reminds you that you have to buy gifts, organize parties, send out cards, get your travel arrangements set, cook, clean, prepare for political discussions with your family members, and everything else.
She also says it's REALLY bad for people who work at stores where they play Christmas music all day for two straight months, because the catchy melodies make it hard for them to focus on anything else.