How comfortable are you with 99.9% effective? That’s the number we like to use to show near certainty. But in a lot of cases 99.9% effective is totally unacceptable. It turns out to be about 3 bad takeoffs from LaGuardia airport per week, 8 failed open heart surgeries a year, or two typos per page in a typical novel. Six Sigma in the strict sense is about getting to a point where you have only 3.4 mistakes per million opportunities. That translates to about 99.999% effective. What a difference a couple of decimal points can make.