If it were done, when ’tis done, then ’twere 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’d 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.
He’s here in double trust:
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,
Not bear the knife myself. 
I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o’erleaps itself
And falls on the other.