The great thing about good songs is that you can make yourself sick of them by playing or singing them ad nauseam, and then go back to them after a while or hear them by accident and fall under their spell. There is something timeless in the structure of a good melody or melody-plus-lyric that engages the higher faculties despite great familiarity with a song. We just need to give it a rest sometimes, go on to new things, then return.