perfection is the enemy of good A different concept, but with a similar ring, is Gresham's law, in economics (could this be what you recall?): "Bad money drives out good."

That is, where multiple currencies are in use (e.g., a medieval marketplace), one currency may be generally perceived as less reliable or more likely to depreciate in value ("bad money"). Merchants will tend to pay for their expenditures with any bad money they hold (to get rid of it), and to hoard whatever better currency they receive. Eventually all the better currency is hoarded and only bad money is in circulation; it has "driven out the good".