Usually used in sports related situations (but also applicable to all life situations), conservation of greatness describes a situation where a person has just done something earth shatteringly amazing, and then immediately proceeds to attempt another amazing action. The second action has 1% chance of doubling the glory, and a 99% chance of failure, which includes a 50% chance of making the person look like an absolute fool.
Popularly used in the game of ultimate frisbee, but possibly originating elsewhere.
'Conservation of greatness' is rarely used as part of a statement, but instead is the entire statement, said after witnessing the the failed follow up action.
Said with great joy when an opposing team fails to compensate for conservation of greatness, but with utter frustration when your own team mate has just made a fool of himself.