I know one reason why Cheers ratings were so bad in the beginning
It was the cold openings. The first season or two had the slackest, dullest, all-around unfunniest cold openings in series history. All the great cold openings people remember came from the third season onward. No wonder Cheers was so slow to win its audience. People tuning in during the first two seasons watched a blah cold opening and thought, "Well, if the rest of the show is going to be this bad..."
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