I’ve always loved this scene, but I feel it’s true meaning isn’t revealed until after seeing the finale. This isn’t just about what’s aired on screen (Ted’s past). It’s about what’s happening in Ted’s present. Ted did not have enough time with Tracy. They were married, they had two kids and she died. Now, Ted has always had a self sacrificial view of love and believes in fate. He wants more time with her. The problem is he can’t and never will be able to after her death. But he still has his memories of her and can relive them when ever he wants. This worries his kids though and they just want him to be happy by moving on. So, he tells them a story using all of his memories, making sure to explore every possible way in which he and Tracy were connected before they even met, proving their love was fate, and justifying his content with reliving the past. What I love about this scene is that Ted is struggling with the concept of love, not as a man distraught with having not found it...but as a father who has had it and is telling his kids he can’t move on from their mother and they should accept that.