In an article in the IEEE Engineering Management Review about dealing with uncertainty the authors noted tension between the positive and negative effects of change. The focus of the article is specific to new product development (NPD), but the principle could apply to most anything. They note that on one hand, "Changes negatively influence internal project success." On the other hand, "Changes positively contribute to project learning."
Since change is inevitable with pretty much anything we humans are involved in, we ultimately have to learn how to accept some level of change. The challenge for each of us is to try to manage change in our efforts so as not to be too damaging to our plans, and to be sure to extract whatever lessons learned we can from changes in order to manage future efforts differently.
Good luck to us all in performing that balancing act. I would suspect that none of us do it perfectly; at least I'm confident that I don't.
If you're interested, here's the paper.
uncertainty.pdf