If you're a sports fan. Imagine that your team loses a lot of close hands. Instead of losing 2-1, 3-2, 4-2, etc., you get to lose one game REALLY badly, then barely win all of your other games. If you lose one game 30-0, and win the rest 1-0, the total goals might be the same, but your win record is suddenly very different.

Gerrymandering is essentially taking a couple of big losses (in voting districts) while racking up many narrow wins. Same vote total, very different outcome.