Susan Feitelberg's - The Net Worth Workout

According to Susan Feitelberg in her book The Net Worth Workout , the average American works 44 years, then retires with a $46,000 net worth ( excluding home equity ).  That represents just $1,000 for every year worked.  Yet, if that person were properly investing $1,000 every year for 44 years in the S&P 500 ( average annual growth of 10% ), then they would have $378,000+.  If that is true, what goes wrong with individual's savings over these 44 years?  I think this tells us that folks are continually dipping into their money without letting it compound properly.  A perfect example is when folks borrow against their 401K plan.  This is perhaps one of the worst things you can do for your long-term financial stability.  I know this is popular and I have made the same mistake myself once, but it's really a poor idea unless it's an absolute emergency.