There are powers that can be invoked and wielded, for a price. When the cause is important enough, you pay that price willingly.
Several hours ago, playing at a wedding reception with
Three Left Feet,
was such a time. The price, you wonder? I'm going to have "Si Beag,
Si Mohr" stuck in my brain for the next week. (It's not as
though we played it a lot -- just thrice through the melody, that's
all -- but with that one it doesn't take much to get it
brainstuck if you play it right, as maugorn, who was on
melody for that tune, does.)