If you’re aiming for Mars, and the trajectory is off by even a tiny margin, you might miss your target by a long way. Likewise, if you’re going to meet someone and they tell you that they left their house and are heading to the coffee shop, it would be silly to still go to their house and expect them to be there.
The point is, sometimes it’s a good idea to change direction mid-flight. It might be that the direction you thought you were going wasn’t quite right in the first place. Or it might be that the destination you want to reach has changed.
The same is true of stories. One member asked if it’s a good idea to change her outline halfway through her story if what she had planned seems boring to her now.