One needs to see something to know it (Typically we cannot know about things until we see the things in action because the words we hear about things are, for the most part mere concepts. (The mind's eye needs a tutor.)
But one needs to know something in order to see it (except if you stumble over it). (We do not recognize “bits” of the Japanese language when we see it unless we just happen to know what is being represented.) In a sense we can't see things we don't know. (We name stars and constellations so that we can see them.)
When we know something, we can locate and see it much faster (because we know what we are looking for and oftimes the thing we are looking for “jumps out” at us).
When we know what to look for or know what it looks like, it can be 1000 or more times easier to see it.
No two people see anything the (exactly) same — but yet we assume, in everyday life, that this is not the case and that others do see what we see (forgetting that much of our seeing takes place in our mind and not in our eye)
Seeing is believing – hence David Copperfield has become quite wealthy and we can be made to believe anything by being convinced that we see it. (DC has convinced many that he has decapitated a woman subject and made the Statue of Liberty Disappear.)