If you are in twenties or early thirties and remain single, earn $3,000 after tax per month, you will probably save $1,000 if you, let's say, spend $500 to $800 on rental, a guest bedroom in a shared house/apartment, $500 on food, $50 on utilities, $150 on phone/internet bills, $400 on commuting costs or gas/maintainance if you have a used car, $200 on occasional entertainment or others. This $1,000 savings will allow you to invest or place a house down payment when time is ripe. Is this possible based on where you live ?
Of course, with those numbers anyone could save not just 30% but probably 50% if that were the objective. The problem of people who do not save is, most of the times, that their income is not great. I am not saying that earning a lot means you'll save, because you can manage to spend it, I am saying that many people out there have just enough for the basic needs.