However, it is recognized that TPR is most useful for beginners, though it can be used at higher levels where preparation becomes an issue for the teacher. It does not give students the opportunity to express their own thoughts in a creative way. Further, it is easy to overuse TPR-- "Any novelty, if carried on too long, will trigger adaptation." It can be a challenge for shy students. Additionally, the nature of TPR places an unnaturally heavy emphasis on the use of the imperative mood, that is to say commands such as "sit down" and "stand up". These features are of limited utility to the learner, and can lead to a learner appearing rude when attempting to use their new language. As a TPR class progresses, group activities and descriptions can extend basic TPR concepts into full communication situations.