Language mastery is based on complex language knowledge and skills. To achieve a high level of proficiency in one language, it is not enough to know many words and know how to apply grammar rules, but it is also important to understand and use specific expressions in that language. The use of expressions allows people to express themselves figuratively more naturally in the target language. Native speakers generally prefer to use expressions rather than producing new lexical combinations. For example, if a native French speaker says "He runs away very quickly", he will tend to use a common phrase such as « Il s'est enfuie à toutes jambes » or « Il est partie en coup de vent », rather than « Il a fui très vite». Similarly, if he wants to describe the intensity of his difficulties, he will be more likely to use the expression « de peine et de misère » than « avec beaucoup de difficulté ». These examples show that to express self-figurations naturally in one foreign language, one must make sentences that are not only in orthographic and grammar, but also able to use expressions frozen (expression figée) in the target language.