Have you ever had a day that was going just terribly and then someone says something that turns it around?
That very feeling is why this song was such a big hit. That, and the fact that Eminem sampled it.
The song itself starts out with a string of bummers - and then makes a super positive left turn. Dido's light and airy, yet powerful voice makes you appreciate the positive message even more.
By the way, Dido didn't go anywhere. She's still around. And still performs what is inarguably her biggest hit song.