DO THE MATH: How Opportunity Costs Multiply Tuition. In my case, the opportunity cost of my doctorate was about $180,000 -- and I worked at least half-time during my entire graduate school enrollment.

I did well during my subsequent career, but even now that I'm retired, I'm still not sure the additional education overcame the opportunity costs associated with it. That said, there are still good reasons for additional formal education -- the challenge is one, and the need to get a ticket punched another -- but earning higher wages is not one of them.