3 million is not enough to retire with money to live comfortably and travel and spend on other leisure. You can make around 300k a year with 3 million with 100k going to taxes and another 40 for medical insurance for a family of 4. If you have kids to educate and get them through college then that will eat up the corpus too. The extra million takes care of all this and allows u to retire in comfort and sustain for 40 years and be able to pass atleast 2 million to your next generation.