You write your proposal. You've got a clear thesis statement and full annotated bibliography. The teacher likes the direction that you're headed and tells you to move ahead. You enjoy finishing up your research and writing the paper. It comes together easily and you feel that you've done a good job. You're reasonably sure that the teacher will feel the same way.
Serendiptiy is a wonderful thing! Especially when you feel like you, as the teacher, might have a hand in nudging that along. In the end, student had to do the work of putting the pieces together and they were either smart enough or lucky enough to see the patterns and make sense of the topic enough to find that focus. Reflective pieces, such as inquiry journals, where a student is required to regularly take a step back from the details to see the forest for the trees, can also help patterns to be recognized and focus to be found.