That depends on what it is. Food, shelter, electricity, water, healthcare, and transportation are inelastic[1] - we buy them regardless of price because we can't live without them. Whether or not we can afford them is largely irrelevant.

Also, don't underestimate change. Buying a house or a car that you can afford now is one thing, but that doesn't mean things won't change in a way that means you can't afford them in the future. Things happen that can negatively impact your income.

[1] http://www.investopedia.com/terms/e/inelastic.asp