In RulesAreMadeToBeBroken, RaySchneider says: "It all reminds me of the moral decision making principles taught by the good Jesuits ... ThePrincipleOfDoubleEffect is one of the most interesting and most misunderstood."

Can someone explain the rule?

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I'm a Dominican, not a Jesuit, but as I understand it the principle states that, If an act has both good and bad (foreseeable) consequences, it is permissible when the following hold: 1) the act is not itself bad; 2) the bad consequence is not intended; 3) the bad consequence is not the means of achieving the good consequence; and 4) the good consequence sufficiently outweighs the bad consequence.

Consider, for example, the question of whether I should hard-code an array size.
This might have the good consequence of simplifying my code, or maybe making it a little faster; a bad consequence is the maintenance cost. 
	1 Hard-coding array sizes is not, in itself, bad, or else defining 3 dimensional points would be bad. 
	1 I wouldn't do it intending to increase maintenance cost.
	1 My code doesn't become simpler because of the increased maintenance cost.
	1 Is simple code worth the increased maintenance cost? Well, in the abstract, who can say? Here is where straight reason yields to prudence, and why RulesAreMadeToBeBroken.
-- TomKreitzberg