What does the phrase two swallows don't make a summer mean?

Perhaps you refer to the saying of Aristotle, in the Nichomachean Ethics: One swallow does not make a Summer; echoed in 1546 by John Haywood in Proverbs as One swallow maketh not summer, and again in 1577 in Northerbrooke's Treatise against Dancing as One swallow proveth not that summer is near. Cervantes repeats it in Don Quixote. Walt Kelly's Pogo remarked it depends on what you swallow.