"But I already know that..."

Whether you're a teacher or a learner, you're going to find yourself looking at certain language points and saying, "already covered that." Which is very nice, but that's not the same as knowing something automatically so you can focus on what you're talking about instead of how you're saying it. This is another reason you should use multiple study aids if you're learning on your own.

For more on learning versus knowing and the dangers of over-optimistic self-assessment, visit the ForeignLanguageBlog, from which the post title was shamelessly lifted.