How I Met Your Mother, Season 8

[Barney tries to explain to Robin why the Playbook still exists]

Robin:
You really think this is just about a book Barney? You lied to me, and if we're gonna be in a marriage and trust each other, you can't lie to me. Ever.

Barney:
Really, well that's just great, because in case you haven't noticed, these last eight years, lying is what I do best. [Begins pulling out various magic tricks] I'm a magician, Robin. Misdirection and deceit are my stock and trade. You don't want me to lie to you? Lies are the reason that we're together. Every single thing I did to you to get you to say "Yes" to me on that rooftop - Patrice, the false engagement, everything - it was all utter malarkey, but underneath ... all of those lies is one true thing - one true thing that can support the weight of all the lies in the world and that's the fact that I love you, and you know that when I say that, I'm not lying.