Ted: Okay. You're ready.
Barney: Ready for what?
Ted: To read the letter.
Future Ted: [v.o.] Kids, the letter was a device I'd invented to remind myself why I'd broken up with somebody. I'd been doing it for years.
[flashback to Ted writing a letter in 1996:]
Ted: [v.o.] "Dear Future Ted, never get back with Karen because she's a pretentious snob. Oh, also, she cheated on you. I'm sorry you had to find out this way. [chuckles] See, we're already laughing about it."
[flashback to Ted writing a letter in 2005:]
Ted: [v.o.] "Dear Future Ted, stay away from Natalie, or any girl who can pin you to the ground and beat you senseless in front of a cheering crowd. P.S. Please consult a therapist about why that turned you on a little bit. "
[flashback to Ted writing a letter in 2008:]
Ted: [v.o.] "Dear Relationship Genius, Stella left you at the altar. You may never love again and will probably die alone." Huh! It doesn't look so sad written in calligraphy.