As I read the question, Archie was not talking about competence and practice, but about giving yourself enough prior exposure to the song so you can be sure you won't be overcome by emotion when you try to perform it.

For myself, there are some songs where I'm never sure if I'll get all the way through: "Foggy Foggy Dew" and "D-Day Dodgers", for example. And I wouldn't even dream of trying to sing Cecily Fox-Smith's "Home, Lads, Home"

And you need a heart of stone to keep from laughing when singing "Nobody's Child".