You don't know what you don't know.
This seems pretty obvious on the face of it, however, upon closer inspection we can see the trouble that is inherent in this statement. There is knowledge that you may never know that will not matter to you in the slightest, it won't effect your life even an infinitesimal bit. Then there is the other knowledge, the things we all take for granted, that affects our lives deeply--we don't know only because we never thought about it.
“The range of what we think and do is limited by what we fail to notice. And because we fail to notice that we fail to notice, there is little we can do to change until we notice how failing to notice shapes our thoughts and deeds.”--R.D. Laing, British psychiatrist
We are taught not to question very much and given knowledge presented as absolutes. These are never questioned, but should always be tested. Much of this known knowledge is in reality simply theory. Tested theories, in many cases, yes, but theories nonetheless. Ask the Wright brothers, Thomas Edison, Albert Einstein, Nikola Tesla, even Galileo, about theories and consensus. Scientists are very good at this, or I should say rather, very good scientists know this and use it. That we have to question the answers:
"...only when we truly realize and accept that we cannot actually know what we cannot see, that we can begin to remove the blinders that this creates. This paradox of embracing the blindness in order to gain sight, is of crucial importance. Yet this insight comes with a price. It is characterized by tireless skepticism and testing. It is themed by such questions as, “what do you base that on?”, and “why?” This state of mind is uncomfortable, difficult to maintain and exhausting, especially in times of stress... Due to all of this difficulty we humans are therefore easily seduced by untested assumptions that promise a wealth of certainty, yet may well end up being the next Ponzi scheme. We are suckers for this. We are human." --J. Michael Bone, Ph.D.
You don't know what you don't know, so you didn't even think to ask. We just assume that what someone is telling us is accurate--or what we read or watch, for that matter. If it is reported, suddenly, it is the truth, when in actuality it is no more factual than shadows on the cave wall:
We are the people in the cave when we let people give us easy answers. When we will not look for ourselves we fall into the trap. Nothing in life, that is worth anything, is easy. It takes courage to take our shackles off and step outside the cave. It can even hurt. Yet, freedom always has a price and, even more importantly, we must see that we are in chains in order to realize we need to free yourself.