If it were done when 't is done, then 't were well

It were done quickly: if the assassination

Could trammel up the consequence, and catch

With his surcease success; that but this blow

Might be the be-all and the end-all here,

But here, upon this bank and shoal of time,

We 'ld jump the life to come. But in these cases

We still have judgment here; that we but teach

Bloody instructions, which being taught, return

To plague the inventor: this even-handed justice

Commends the ingredients of our poison'd chalice

To our own lips.

William Shakespeare (1564-1616): Macbeth. Act i. Sc. 7.