This pattern is used when you want to say that something is not easily done, or that a desired result is slow to come. It often carries a feeling of impatience or surprise. For example, if you are waiting for a bus that is always late, you might say, 'バスがなかなか来ない' (The bus doesn't come). It emphasizes that the action or state has not been achieved despite effort or expectation. なかなか is placed before the negative predicate. It can be used with verbs (e.g., なかなか覚えられない), adjectives (e.g., なかなか寒くならない), and also with ない in other forms like なかなか無い (rarely exists). Note: When used with a positive statement, なかなか means 'quite' (e.g., なかなかいい), but with a negative, it has this meaning. So be careful with word order.