The labour we delight in physics pain.
– William Shakespeare
Macbeth, Act 2, Scene 3. Macbeth says this to Macduff, after offering to bring Macduff to King Duncan and Macduff responding that hosting the King must be a “joyful trouble” to Macbeth. What Macbeth is saying in this line is that work we enjoy cures the pain involved. Since the audience knows that Macbeth has murdered Duncan and is pretending otherwise, this is dramatic irony.