Future Ted: [v.o.] So, when Barney and Robin broke up the previous fall...
[flashback to fall 2009:]
Barney: Dating Robin was a huge mistake.
Ted: Write that down.
Barney: What?
Ted: Write yourself a letter. That way, when you miss Robin, and you will, you can remind yourself why you broke up.
Barney: Gladly. "Dear Future Barney..."
Ted: Ooh!
Barney: This ink is cool.
Ted: Right? Right?