Your internal values/beliefs/preferences, sure no one can tell you what those are. But your preferences that are manifested externally, that's another story entirely. You don't get an objective view of yourself from the outside the way many of the people with which you interact do.
Here's a long-winded example (no pun intended):
Let's say that you are the kind of person that is easily influenced by your environment and peers. You happen to make friends with a lot of people who are into skydiving (not because they are into skydiving; it's just happenstance), so you become of the opinion that skydiving is cool and hip and in order for one to be "cool", one must enjoy skydiving. You are going to tell yourself that you like skydiving, and you will probably force yourself to do it, since all your friends do it too; it's your way of fitting in. So, in a test that asks "Do you like skydiving?", you'd probably convince yourself that the answer is yes, and fill in the bubble accordingly. However, your friends see that it scares the living daylight out of you everytime you are standing in the doorway of that plane, and when you are outside of this social context, you never take it upon yourself to pursue your "hobby." You really don't enjoy skydiving; you've just managed to convince yourself of this due to peer-pressure related circumstances. Your skydiving friends and your other friends outside of the SP skydiving circle realize this because they view your actions objectively; they see that you get the sweats everytime you are in the plane, and they see that you never actually initiate skydiving endeavors. Your other non-skydiving friends realize that if given the choice, you'd rather be doing something on the ground, and they've never heard you convincingly talk about the thrill you get from skydiving. Therefore, in this situation, I'm of the opinion (and you may argue with me on this) that your friends would be better suited to more accurately answer the sky-diving question on a test. Now, I know that these type tests don't typically ask "Do you enjoy skydiving?", but they do ask many other tangible, external, behavioral questions that point to certain internal preferences, and many people will answer wrongly on these tests because they have essentially convinced themselves of a lie. In this instance, admitting that you enjoy skydiving points to a strong Se function, but really it's a manifestation of wanting to have a sense of social cohesion, or Fe.
Now, I know that you are reportedly an Ne-dom guy, so you don't really understand what it's like to be under the influence of social pressures. You value your own personal, unique forms of expression, and fitting in is not of high importance to you, so you are probably a bit more capable of being honest with yourself. However, not all people are of this philosophy, and many will indeed answer inaccurately in self-report because they don't have this sense of self-validation.
I actually read about a psychological study that is highly related to this topic. I'll see if I can find a link to it.
