Allegedly that's the reason why people learn faster when they are abroad and have a contact with native speakers than when they study from books/casettes.
Not only that, but they can't rely on their native tongue while there. They are completely surrounded by a different language and culture so the mind has to conform or won't be able to get around very easily.
This accute adaptation strategy helps the mind to get in the habit of using the foreign language instead of the native one.
Once the mind is in the habit, it becomes easier to think in the new language.