The Four stages as identified by Melissa Alexander, a respected clicker dog trainer are:
1. Learning the Behavior
2. Perfecting & Generalizing the Behavior
3. Applying the Behavior
4. Living the Behavior
Of course, all of us want to be on the last stage stage 4 yesterday, but in reality, for some tasks it may take many months or more to get to that point. It is critical that you spend the time on the earlier stages to ensure your dog is ready for later one as they all build on each other.If you get the stage 4 and you find your dog is making many mistakes, it is more likely a factor of speeding through previous levels, rather than your dog's inability to do the task (unless of course he is physically unable to do it.)
Here is a link to Ms. Alexander's original article where she discusses each stage.