End of a predictable story: "flat" or "plain"?

I am looking for an adjective which could work with the "end of the story", meaning predictability, shallowness. Now I am deciding between "flat" (in Freedictionary 5th,6th, and 12th explanations work well) and "plain" (because it helps to transfer the obviousness, simplicity). Unfortunately, I can't really see the difference between the two synonymes. What would you advise to focus on?


Solution 1:

Of the two words you are considering, I would choose flat.

As in: Writers Relief

How To Write A Happy Ending That Doesn’t Fall Flat