I disagree with a lot of the reactions on here, in the sense that I just really think the ending was rushed and bad writing, not logical and/or reflective of real life. I'll shortly explain why:

People grow, that's also part of life: Barney and Robin grew during the show and became both more adult and worked on their flaws. At the end of the show all the “wrong traits” they displayed they outgrew or were outgrowing them. Of course there would be setbacks and a marriage isn't always easy, but Barney and Robin were clearly ready for it. We didn't watch over 2 seasons of character development and build-up, too see them divorced. Their divorce was very bitter and way too rushed. Why build a whole season around a wedding, to basically state in the final episodes the whole wedding was bs anyway and divorce the bride and groom. Barney and Robin basically became who they were in season 1 and it was incredibly sad and unfulfilling to watch. It basically told us that you are always the same person and now matter how hard you work and what you go through, after a setback it will all be reverted and you'll end up basically the same. It's incredibly bitter, cynical and even unrealistic.

The ending didn't do right to Tracy's awesomeness: Why did Tracy have to die so soon and why did Ted have to end up with Robin after all. Ted being married to Tracy was given little attention and even though she was perfect for Ted, she had to die. Just the fact Tracy had to die to make way for Robin is lazy writing and it wasn't executed well at all. I thought it was very sour how Tracy's character was treated by the writers. Of course the message wasn't bad: life is full of ups and downs, there is no such thing as the one, treasure every moment with someone you love etc. But we watched every single relation of Ted fall apart, too see how his wove dies in the end and he ends up with the girl he could've ended up with years earlier. Nah, I would have preferred Ted having a happy ever after.

If Ted and Robin were meant to work, this should have worked earlier:

Why didn't they get together earlier if they were supposed to end up together? Ted and Robin were perfect as friends. They shouldn't have forced this relationship up too people at the very end after showing us why it wouldn't work 9 seasons long.

Barney and Robin both had a partner that could've been their soulmate (Kevin and Nora), who they betrayed for each other, having them divorce meant they ruined their chance for happiness with these other people (especially Barney could have been very happy with Nora) :

Why did the writers choose to split up Barney and Nora and Robin and Kevin, too make way for Barney and Robin, if Barney and Robin were meant to divorce in the end? Why couldn't they just have been happy with their other partner? Especially Barney could've had a very happy future with Nora.

If Barney and Robin's relationship was too toxic to work, it shouldn't have gotten to a wedding at all and the divorce should have happened much sooner than three years:

Why drag it out to a wedding and after the wedding for three years? If they shouldn't work, don't make a whole season about how well they work and than break them up anyway.

Conclusion: the writers had an ending in their minds from the starts and rushed events to fall in line with their prerecorded ending, instead of altering the ending to fit better in the natural way the show had developed. I find this very uncreative and in the end the writers realized their mistake and tried to cut it out anyway, so yeah…