Whether you write to an outline, or churn it out by the seat of your pants, all of us are likely to come to a moment in the creation of a story where we are struck by a realization: if character X only did this instead of that, it would be so much better for the story.
How much trouble this causes you chiefly depends on how far along you are in the story at that point. It may cause you to revise your possibly painfully detailed outline, or it may force you to reconsider exactly where the story should be headed, if you're not confined to an outline, thus revising some of the highlights to come.
As a pantser instead of a plotter, I find this mostly happens to me when I brainstorm “what next?” for the moving boundary of the current words, but it can strike for older character actions, too, further back in the body of work.
I don't know about you, but my typical reaction when this happens is first elation (whoopee — an improvement!) followed by depression (look at all the changes I'm going to have to make to what's already been done and what is to come). Generally the former outweighs the latter, but I do have to get past the moment of deep despair at the work involved.