The problem is, to quote John Maynard Keynes once again, "Practical men are usually the slaves of some defunct economist."
To put the problem of these "practical" — aka "common" — men in more practical terms here's iconoclastic economist Thorstein Veblen presciently explaining the situation:
...the ownership of property in large holdings now controls the nation's industry, and therefore it controls the conditions of life for those who have to resort to the markets to sell or buy. In other words, it has come to pass with the change in circumstances that the rule of Live and Let Live now waits on the discretion of the owners of large wealth. In fact, those thoughtful men in the eighteenth century who made so much of these constituent principles of the modern point of view did not contemplate anything like the system of large wealth, large-scale industry, and large-scale commerce and credit which prevails today. They did not foresee the new order in industry and business, and the system of rights and obligations which they installed, therefore, made no provision for the new order of things that has come on since their time.
...the population of these civilised countries
now falls into two main classes: those who own wealth invested in large holdings and who thereby control the conditions of life for the rest; and those who do not own wealth in sufficiently large holdings, and whose conditions of life are therefore controlled by these others. It is a division, not between those who have something and those who have nothing — as many socialists would be inclined to describe it — but between those who own wealth enough to make it count, and those who do not.
A vested interest is a legitimate right to get something for nothing, usually a prescriptive right to an income which is secured by controlling the traffic at one point or another... is common in the respect that he is not vested with such a presciptive right to get something for nothing. And he is called common because such is the common lot of men under the new order of business and industry; and such will continue (increasingly) to be the common lot so long as the enlightened principles of secure ownership and self-help handed down from the eighteenth century continue to rule human affairs by help of the new order of industry.
http://inspectorlohmann.blogspot.com/2006/12/building-invisible-comic-community.html