A strategic plan will change more frequently. For example, if a goal is to lose weight and the weight loss is achieved, now the plan will change to maintenance. If computers skills are needed and I have learned word processing, now I may need to learn a spread sheet application or the internet. The mission statement goal may remain the same but the strategic plan allows me to grow. Remember, however, things that are too rigid, break.
Flexibility is good, maybe even crucial to survival.
I have learned in recent years that one of the great constants in life is change. While my mission statement has remained fairly constant since I first wrote it about five years ago, my life and strategic plan have changed substantially. Five years ago I thought I could predict fairly accurately what would happen in my life for the next 20 years or so. Past experience of prior generations led me to believe life would be routine, settled and happy. Happy fortunately, yes.