As soon as Macbeth colludes with sorcery, he is troubled by the difficulty of reading the future. As a loyal thane, Macbeth could let others worry about the scatter from the future's riddle; but in a state of disobedience, Macbeth must learn to haruspicate or scry for himself, in order to ponder the means against the ends.

Do the ends justify the means? If a German man had killed Hitler in 1933, could he have defended his act? The assassin might argue that Hitler's policies would lead to the extermination of Europe's Jews, the death of millions of soldiers, and the ruin of his own state. On the other hand, it is likely that such a defense would have availed nothing, since Hitler was a democratically elected head of government, personally guilty of few demonstrable crimes; and furthermore, no jury in 1933 would have been likely to credit the dire consequences of Hitler's rule that the assassin foresaw. It is only in retrospect that we know the consequences of human acts; but we must make decisions in the present instant, when the future is simply a confusing heap of probabilities and possibilities. This is one reason why ethicists are always suspicious of the argument that the ends justify the means: we can weigh the virtues and vices of the means, but we can’t weigh the virtues and vices of the ends, since the ends lie in an indeterminate futurity. In 1933, it was possible to hope that Hitler might mature into a wise, prudent, responsible leader; only with the help of a time machine can we hope to ascertain the ends, and therefore to be able to measure their good and evil against the good and evil of the means. Only someone certain of future events can be certain that an end justifies the means that accomplish it.

Macbeth is a play about the consequences of action; a play about squinting into the future to guess at the consequences of action. Macbeth is not like a 1933 assassin of Hitler, in that Macbeth is not trying to do the greatest good for the greatest number—he's only trying to do the greatest good for number one.