Do you need to just start from scratch on a problem?
Scrap what you already “think” you know or what you have compiled on the person. While going back to before you knew anything about the ancestor in question is not usually possible (after all, can you really intentionally forget what you know?). But there are some things you can do with the information you have already collected.
Go back and and make certain you have completely and accurately cited each record mentioning your problem person. Review those records and analyze carefully each piece of information you have discovered–paying particular attention to clues or names you may have overlooked originally. Write down each step in your logic and reasoning.
Maybe even argue with yourself slightly as you work on the problem. Question yourself.
Sometimes what we need is just a fresh start.