I was talking to the late and much lamented Jake Thackeray some years ago and I asked him why he never sang 'Isobel makes love on our national monuments' any more. His answer was most illuminating. He told me that the last time he sang it, halfway through he was thinking about replacing the glass in his garage window at home and was thinking to himself if he had enough putty. He realised that the song meant nothing to him any more, he could sing it without thinking about it and as if he was on auto pilot. So he just stopped singing it.

I think the moral is, learn your song, learn it well, but know when to stop singing it.