Shrinking racers since 1992, the lightning bolt is one of the most powerful weapons in all of Mario Kart. It's truly an unbiased punisher, rendering all but its user into miniature and flatten-able targets. I've often compared Nintendo-made multiplayer games to socio-economic classes, and Mario Kart is no exception. In this case, at the top lies either a single player way ahead of the pack, or a small group constantly trading the top spot amongst one another as the result of random item acquirement or blowback from the lower classes. In the middle lies most of the racers, struggling and battling fiercely amongst each other with the goal of achieving first place. In reality, they can only be the leader of their own group. Once in awhile a single racer by chance manages to find his or her way into the top tier, which only serves as motivation for the other middle-classers to continue struggling against one another. And at the bottom lies the proletariat; a group destined to round out the bottom.
While the lightening bolt item will certainly cause dismay in a tightly-woven group, a clear frontrunner will usually not lose first place because of it. Indeed, it seems that no item from the lower classes can ever consistently dethrone those at the top ... with one exception. It is perhaps the greatest move that can occur in any video game. On an extremely long jump (think jumping over the steam boat in Mario Kart 64), you manage to fire off the lightning bolt right as the first place person is in mid-air. The shrink will cause them to lose all momentum in mid-air, sending them to the ground below and surrendering first place to whoever is next in line. It's truly a beautiful moment.