A breakpoint is when you earn $X, and that's low enough to get $Y in welfare. But if you work longer/harder the total amount you get is still $X+$Y because your welfare amount is reduced dollar-for-dollar with your earnings above $X. You don't start to increase your income unless you manage to earn more than $X+$Y entirely on your own. This creates a huge disincentive to earn more than $X, because for most people at that income level the jump to earning $X+$Y seems insurmountable.