Quotations and aphorisms by Kenneth Arrow:
That economic decisions are made without certain knowledge of the consequences is pretty self-evident. But, although many economists were aware of this elementary fact, there was no systematic analysis of economic uncertainty until about 1950.
The major driver of economics is the equilibrium approach, which has taken various forms over the years. General equilibrium is the statement that all the different parts of the economy influence each other, even if it's remote, like mortgage-backed securities and their demands on automobiles.