I usually divide someone's salary by their hours worked before getting envious. Some people work crazy overtime. 70 hour weeks aren't my idea of a good life, no matter how much you make.
I then think about their investment in their education--MBA, law school, med school? Then I consider the fickleness of the job/income source. If you make $200,000 one year, and nothing the next because you were laid off, that's $100,000 per year, not $200K.
I consider the location of the job (Southern California? New York City? San Francisco?) where taxes and housing alone are the highest in the U.S.
Some jobs pay well but are very unstable and/or have limited benefits. If all you get is cash, and no benefits, then health care, retirement, time off (sick, vacation) is out of your pocket. Private contractors in Iraq are a good example of a highly paid, but unstable job. Envious soldiers merely compare straight salaries, not the benefits and the odds of being unemployed in a year.