This phrase is subjective and often used for personal opinions about what is enjoyable or important. You haven't lived until you've gone skydiving.
Pro Tip 2/3
Hyperbolic
The phrase is hyperbolic, meaning it exaggerates for effect, not to be taken literally. If you haven't seen the Grand Canyon up close, you haven't lived!
Pro Tip 3/3
Conversation Starter
Often used to spark conversation or share experiences with others. You haven't lived until you've tasted my grandma's apple pie.