Thou wouldst be great;
Art not without ambition, but without
The illness should attend it.
– William Shakespeare
Macbeth, Act 1, Scene 5. Lady Macbeth accepts that her husband is not lacking in ambition. But she is afraid that he doesn’t enough wickedness – “the illness” – to achieve greatness. Determined that Macbeth will be king, she doesn’t know if he has the killer instinct to do what needs to be done – kill Duncan. “Illness” is a metaphor for the ruthlessness needed to commit regicide.