It may mean not going out to eat all the time, not buying a fancy new car all the time, not having a fancy house in the most prestigious neighborhood, etc. I'm not saying it's bad to buy or want these things, but they are luxuries you pay for with hours in the office.
Early retirement is even easier if retire doesn't mean, "never work for money again", and instead means, "I don't have to take salary into consideration when deciding when/where to work". I'm an engineer living in the SF Bay area who doesn't make tech money and I'll still be able to retire after 15-20 years, easily, while still having waaaay more than my parents did when I was growing up.