Why does the stretch between Thanksgiving and Christmas make Greg nervous?

Although most people look forward to the holidays, Greg feels very nervous during the time between Thanksgiving and Christmas. If he makes a mistake the first 11 months of the year, it is no big deal. If he does something wrong during the holiday season, he will pay for it. He thinks it is too much pressure to be on his best behavior for a whole month, which is necessary if he expects good presents for Christmas.