Why is ‘x’ the unknown? :: Lean Sales and Marketing thru Service Design Thinking – Businessweek

I have always believed that history was important. And if you are in the quality field or more specifically a Lean Six Sigma person it is hard to believe that “X” is not important to you. Why is ‘x’ the symbol for an unknown?

Source Article from http://bx.businessweek.com/lean-six-sigma/why-is-x-the-unknown–lean-sales-and-marketing-thru-service-design-thinking/18266900420389897150-8773cdd292fea52a1e890938f92e1f68/