I went back and looked at our (me and spouse) records for incremental savings over the past decade. Soon after we purchased our house we put together a more focused plan - nothing fancy - same as much as we could in our tax-deferred 401 and 403b plans, don't spend much, generally be frugal with vacations.
So the numbers - in 2006 we had $235k in investments and cash, a $200k mortgage, and a daughter getting ready for college. In 2016 the kid has been out of college, did some remodeling, we paid off the house (now worth upwards of $700k), purchased a decent used car and a new one with cash, and have $1.2M in savings. Two more years of working FT will be enough. So it's possible.