It's amazing how just one word in a song can change the mood instantly. Take Seasons in the Sun.
We had joy, we had fun,
We had seasons in the sun,
But the wine and the song
Like the seasons have all gone.
Notice how the spirited first two lines have their mood changed almost instantly by the word But to one of melancholy, even loss. One might think the content - 'wine', 'song', 'all gone' - establishes the new mood, but no, it's entirely the work of that one word. And if you don't believe me, notice how the same thing happens in the school parody of the song:
We had joy, we had fun,
Flicking bogeys at the sun,
But the sun was too hot,
And our bogeys turned to snot.
It's remarkable how the But mood change works even with nasal mucus.