David Henrie, who plays Ted’s son, said that on his first day, he and the daughter shot some of what could be the series finale. The creators had an idea of how they wanted to end it all. When asked if the fans will like the ending, Henrie said, 

“100 percent! It’s a great ending to the show. It’s solid and well-thought out from the very beginning. We’ll see if they end up going with it, but I think fans would really appreciate the ending.”

Now here comes my theory:

“Solid and well-thought out from the very beginning”. Ted started off the series telling his kids the story of how he met their mother. It wouldn’t make any sense to start the story on a random night, it started on the night that Ted met Robin. This night was not just a random night in Ted Mosby’s life. If there was a possibility that she was the mother, it would make sense to start there, right? But she isn’t the mother, so why start then? Because we now know that Ted meets the mother at Barney’s wedding. Barney Stinson was a man who would never commit and was disgusted by even the idea of marriage. It would take an amazing woman to change that. He would have to meet someone worth changing for. Ted would have had to meet Robin, so she could meet Barney, so they could have a wedding, so Ted could meet the mother there.

I truly believe that Carter and Craig have had that plan all along. They’re too smart. They’re not just going to throw some random girl in there who’s going to be able to make Barney Stinson commit. 

My faith in Barney/Robin is not blind. The show just wouldn’t make sense otherwise.