The science of economics, therefore, is difficult on four counts.
The economy itself is exceedingly complex;
the economist is subject to the pressures of various interest groups;
like everyone else, the economist may early acquire tenacious prejudices about economics which are very hard to get ride of; and finally,
the economist is not free, as are the practitioners of many other sciences, to make controlled experiments. — Lorie Tarshis (1947)