Yesterday I had a chance to look over a textbook of one of the most famous English schools in Japan. Like other textbooks of English, there were a lot of exemplary sentences. There was one with the phrase "a world of fish," and it was translated as if the phrase means the place where fish live and prosper. But the phrase "a world of sth" is used to emphasize the number or the quantity of something. In other words, it means almost the same as "a lot of."
What can be learned from this incidence? (In the following the pronoun "you" denotes me. I am talking to myself) First, ignorance itself isn't very detrimental. But ignorance of your ignorance can cause you a world of trouble. For it can lead you astray without your realization of the fact. Second, a dictionary is as good as the best teacher in Japan. Always have a dictionary at hand when you study English. And if you feel that your understanding is slighly vague, be sensitive to that vagueness and consult your dictionary.