The fastest driver always has the biggest target on his or her back. In the real world, this applies to speeding tickets and douchebags in tricked-out Civics who want to race. In Mario Kart, the stakes are even higher. The lead cars always have to keep an eye out for turtle shells flying in their direction.
Seasoned players know that sometimes you are better off sitting in the middle of the pack until the last leg of the race when it's finally time to make your move. Really, this is a lesson that can apply to almost any walk of life. Everybody is hungry to take down the king, so once you finally take the lead, you have to keep your wits about you.