This happens so easily, even those of us who are frugal to begin with. Lifestyle creep is too easy if you are not vigilant. You can easily make your self service poor, cell phone, cable, internet, streaming video, stream audio, subscription services. That is all before the pitfalls of new cars and "upgrading " houses every 3-4 years.
Debt is easy to obtain, but gets harder to maintain.
Oh, lifestyle creep is in full effect at my workplace. Nobody understands the concept.