How much of their money goes to taxes and the impact paying those taxes has on them.
You cannot judge the tax Burden based on what group pays the most taxes, because that number is determined by two things:
-Amount of money available to be taxed
-# of People within that Group.
Which speaks more to the size collective wealth of that group, moreso than the impact it has on them or what % each person on an individual basis pays in taxes.
Tax Burden is an individual metric, that has to be looked at first by the magnitude of economic impact and then by the % of income that goes to taxes.
For example: a Single Person (With no children) who makes $56k/yr has 25% as their top marginal rate, whilst two married people (w/o kids) who earn $56k/yr together have 15% as their top marginal rate.
The Married people get to keep more of their income, than the single person - which means the single person is getting taxes for not being Married AND has a heavier tax burden to bear.
That's what Tax Burden is all about.
E.g. Warren Buffet may pay a lot more of the total tax collected than a family earning $40k, but the family earning $40k would benefit more from a tax break than Warren would.
That must be why Warren thinks that it would be best for the economy if taxes were raised on the Wealthy, or why he protested the cut in Dividend Tax (Even though he's the one who would benefit more than anyone in the Country) and instead cut the taxes of middle income earners, as it would help Business as a group that is low on disposable income would have more and it would help cut deficits and strengthen the dollar/reduce our reliance on foreign capital.
But I'll let the Conservatives School Buffett on Economics.