Politician: A government that taxes incomes at a rate of 100 percent will generate no revenue because all economic activity will cease  So it follows that the lower the rate of income tax, the more revenue the government will generate by that tax
Economist: Your conclusion cannot be correct, since it would mean that an income tax of 0 percent would generate the maximum revenue
arguing that the principle derived by the politician, if applied in the limiting case, leads to an absurdly false conclusion