Ted Moseby was pretty happy in life. He and Robin were dating, and things we're going well. His best friends Marshall and Lily were back together, and just as happy as ever. The only person not happy with this was Barney, who was annoyed at the Couples never wanting to go out and be 'legendary', and instead just be boring and watch TV.
Ted, Robin, Marshall and Lily were having a boring night. They had gone out to McLaren's Pub, but quickly retired to the apartment, where they drank (maybe a little too much), talked and settled in front of the TV.
Robin had drifted off to sleep, draped over Ted, and not looking all that glamourous as she quietly snored, drooling slightly and her hair messed up. But to the hopelessly romantic Ted, this was the most beautiful sight in the world, and he soon fell asleep next to the woman he loved.
Not long after Ted awoke, he had heard a noise. Was Robin awake? No, she was still sleeping. Ted looked over and saw that Marshall and Lily were moving. Through the light of TV, Ted realized that Lily was on her knees, and was looking to get Marshall some happy sexy time, while he sat in the arm chair anxiously trying not to make a noise.
This wasn't the first time they had had 'relations' while Ted was close by, they had been friends for years, and Ted always joked he had been around for ALL the big moments. But through all of this Ted had never really 'seen' anything, and try as he might, he had always thought of Lily Aldrin as crazy attractive. So, while Robin slept on him and against his better judgement - Ted stayed quiet.
