This paper reports an in-depth observational study looking into how two learners, with different levels of competence in Chinese writing, went about using an online database for improving their writing of Chinese. The two learners were given a task to correct some erroneous sentences, which requires them to consult a large repository database of authentic sample sentences with common errors and suggested modifications. Interestingly, it was found that the more competent learner could quickly identify the categories of errors and devise a strategic plan on what to look for. In contrast, the learner weaker in Chinese failed to notice plausible errors and could only search for the given sentences in a pattern-matching manner. This indicates that simply providing the database as such to the learners is not enough and further the facilitation of the instructors to help learners to learn to identify the errors is far more important.