If one neighbour earns more than you, it doesn’t change your bills. But if a large number of people in your area start earning more, and you don’t keep up, you

If one neighbour earns more than you, it doesn’t change your bills. But if a large number of people in your area start earning more, and you don’t keep up, you are going to find it hard to continue living in that area because local prices will reflect the increased wealth. And if you rent you’ll likely be unable to afford the rent rises that are sparked by the increased desirability of the area. That’s my best guess at what GP meant.