Penny and Luke wouldn't exist without 'Let's go to the Mall'

  1. Robin Sparkles creates hit song 'Let's go to the mall'

  2. Being a major success, Robin Sparklea creates the emotional piece 'Sandcastles in the sand', featuring Simon

  3. Robin is wildly in love with Simon, only to be broken up with.

  4. Years later, Simon returns and Robin dates him again, turning her back into a naive teenager only to be broken up with again.

  5. Barney sleeps with Robin as she's so upset.

  6. There is an undeniable sexual chemistry and they date.

  7. They break up, are friends, then Barney elaborately proposes and Robin says yes.

  8. Barney and Robin get married.

  9. At the wedding, Ted sees Tracy, then at a train station, Ted walks up to her

  10. They date, get married, have Penny and Luke.