Understanding Inconsistency

As I continue to read about ADHD there is a lot of focus on inconsistency- but to me this seems like an extremely vague reference. Does it apply to everything or is it primarily applicable to task completion or forgetfulness. Is it a matter of saying one thing and doing another (ie- lets go to the movies, but when you leave the house you are headed in a completely different direction actually going away from the movie theater?).

Your personal experiences and examples would be appreciated. My intention is not for this to become a rant thread- instead just an explanation of some of the manifestations of "inconsistency" to help those of us who are just beginning to understand and learn about ADD/ADHD.