You know more about yourself than you know about anyone else. You might know more about yourself than you know about everyone else put together. But how well do you know yourself, rather than know about yourself? That is, how well do you understand yourself rather than just know facts and details about yourself, why you are who you are and why you do the things you do, rather than just what you are and what do you tend to do? The former, most will probably find much more challenging to articulate, despite a lot of information available to the latter that is like data to support the former, but that may be difficult to interpret to articulate the former.
Despite having lots of information about yourself, unlike most problems in science and life, this excess only makes the puzzle that is you harder to resolve. In fact, you might even think you know yourself less than you know others despite all the information you have about yourself! However, that perception would only be due to your oversimplification of others since they may or may not be any more or less complex to themselves than you are to yourself, despite how they might come across to you and others as being simple or complex. Regardless, the complexity that is each of us is the reason why each of you are the greatest puzzle you will ever know.