With a merely 1% advantage in blackjack, most casinos make countless millions from unsuspecting gamblers. They don't win 1% of the money bet. They win most of it. With a 1% handicap. Or, I can have a balance and scales with perfectly balanced weights on either side, and even if both weigh a literal ton, a few grains of sand on one side will cause that side to sink all the way down. Similarly, in a state where, say, 51% of voters in a given election vote democrat and 49% vote republican, gerrymandering can ensure that republicans still sweep the state by merely shifting the handicap by 3 percentage points.
This wouldn't be such a problem if the result of such an election produced someone who is 52% republican and 48% democrat. But those results produce someone who is typically much more skewed to the values of one party over the other. By winning 1% more of the vote in a district, one side wins the entire district. That's why a very small handicap can result in very big wins for one side or the other.
To be clear, this is or should be a bipartisan issue. The dems got away with it for years, and now the republicans have turned the tables. And one day, the dems will turn those tables again. I hope not, of course. The cure for any kind of imbalance is always balance, not retaliation.