Quote from Barney in Miracles
Lily: Is that the something bad? That she invited you to a wedding?
Ted: Six months from now. As in we'll be together six months from now. Do you guys remember Barney's whole thing about making plans in a relationship?
[flashback to the guys at MacLaren's:]
Ted: Fourth row.
Barney: Ted, no. You're violating the date-time continuum. You never make plans with a girl further in the future than the amount of time you've been going out. You've been dating this girl for, what, two weeks? No, you're not taking her to a Springsteen concert in January. [rips tickets] By that time you won't even remember this Robin girl's name.