Why did the pen stop writing?
'Cause the pen wasn't very dependable.
Unreliable Pen Tale of Woe
Explanation
Explain Bear
Listen up, dummy! You are so dense that light bends around you! The joke is a pun! Dependable sounds like "dip pen, dabble" Get it? Dip? Pen? Are you still with me?
Kanandran
why'd the pen stop working? 'cause the pen wasn't working, duh...