Imagine a story which ends with the hero failing. Okay, personally I actually quite like this brave storytelling decision nowadays. At the same time, I can’t imagine Star Wars Episode VI Ending with the empire winning rather than the rebels . It wouldn’t be the story we all love.
Likewise, in the Story Brand framework “Ending in success” is an important step. Showing the change from before the character met your guide (customer met your brand, the person joined your church) shows that success.