Rules of Programming: Be Open To Change
As important it is to leave your code open to change, as important is it that you are open to change. In our world, changed requirements are very common, thus, we as developers, need to adapt.
The dream for any developer would be to have a full specification and start planning and programming from there. However that's very rarely the case. Customers change their minds, you come up with new and great ideas, and so on. It surely can be a pain with these changed requirements, but it's probably for the better good.
If we can't beat them, join them. We have to be open minded and welcome changes.
Rule #17 of programming:
Be open to change