When 4 isn't 4...

As with all rules of thumb, they work sometimes but over time, things change.  But as the saying goes, the more things change, the more they stay the same.

However, with all rules of thumb, it's a starting point.  The keys are understanding, planning and maintaining flexibility.  Rules are thumb are not meant to be blindly followed.

The 4% rule isn’t broken; it is just badly misunderstood

http://www.cnbc.com/id/102165628