Most plain girls are virtuous because of the scarcity of opportunity to be otherwise.

-Angelou, Maya originally MayaJohnson
  I Know Why The Caged Bird Sings, ch.35

Possessing utility, commodities derive their exchangeable value from two sources: from their scarcityand from the labour required to obtain them.By far the greatest part of those goods which are the objects of desire, are procured by labour.

-Ricardo, David
  Principles of Political Economy andTaxation.

Economics is the science which studies human behaviour as a relationship between scarce resources and ends which have alternative uses† It does not attempt to pick out certain kinds of behaviour, but focusesattentionona particular aspect of behaviour, the form imposed by the influence of scarcity.

-Market
  An Essay on the Nature and Significance of Economic Science, p.16^17.