When a linguistic item is used as the result of faulty or incomplete learning, the learner is considered to have committed an error. A distinction is sometimes made between an error and a mistake. A mistake refers to a performance error that is either a random guess or a 'slip of tongue' , and it is a failure performance to a known, system. Everyone makes mistakes, no matter in a native language or in a foreign language. As we can see that a mistake has nothing to do with the language competence, but a result from a temporary breakdown. When a mistake is challenged or given enough attention, it can be self-corrected. An error, on the other hand, has direct relation with the learners‘ language competence. Errors do not result from carelessness nor hesitation, but lack of knowledge in the target language. Language errors cannot be self-corrected no matter how much attention is given.