Cyril Northcote Parkinson made the following observation in a humorous article he penned for the Economist magazine in November of 1955:
"Work expands so as to fill the time available for its completion."
While the original intent of the statement—and related article and book—was to "explain" (satire) the inevitability of bureaucratic expansion, the statement is valid in almost all situations. This statement is now popularly referred to as Parkinson's Law.
Parkinson gave the following example in his original article in the Economist, November 1955:
"It is a commonplace observation that work expands so as to fill the time available for its completion. Thus, an elderly lady of leisure can spend an entire day in writing and dispatching a postcard to her niece at Bognor Regis. An hour will be spent in finding the postcard, another in hunting for spectacles, half-an-hour in a search for the address, an hour and a quarter in composition, and twenty minutes in deciding whether or not...