Wait until you are in your mid-fifties with no job, no savings left, a house lost to short sale or foreclosure, and no prospect of finding employment. It's easy to say lower your expectations, but for the people I know in this position, that does not cut it. Yes, in retrospect, for many of these folks it would have been better to cut the house and cars loose, quit paying for the kids' college educations, etc. early on, but these people had never been unemployed for longer that a couple of months in their lives. They made what they thought were reasonable decisions at the time. Peak earning years? Not if your job has been shipped overseas, your skills are no longer adequate in the market place, or there are just not enough jobs for everyone.
The premise of the MMM approach is that you save a very high percentage of your income. If you can't pay more than the basic bills on the income you have managed to cobble together, you can't save. These folks will be living on Social Security when they reach retirement age.