This title is based on the well-known expression 'eyes wide open'. If you do something with your eyes wide open it means that you are fully aware of the potential consequences of what you doing. Why do the words 'wide' and 'open' come after the noun? I think it's because they are adverbs, not adjectives, in this expression. 'I like to drive with the windows fully open and the roof right down.' These are all adverbs, I reckon.

Here's why you don't understand the title: it doesn't make sense. The phrase "Eyes wide OPEN" is an idiom. It means "to begin something difficult, fully understanding the difficulties." The grammar of "eyes wide open" is that the phrase "wide open" acts as an adjective, describing "eyes." I'm not a grammarian so I can't really analyze "wide open." But I'll note that "wide-open," with a hyphen, is actually a good English word meaning "completely open." Movie titles are not like section headings in a textbook. They're supposed to catch your attention. This phrase catches our attention because it's the opposite of what we expect. Your first reaction is "Eyes wide SHUT? What on earth can that possibly mean?" The meaning is whatever you read into it. Nothing in the movie makes it any clearer. Maybe it means that these characters think they are going into a situation "with eyes wide open" but that really their eyes are shut. Don't expect clear English in movie titles, book titles, or song lyrics. Here are some other examples of famous titles in English that don't make much sense. They don't make sense when you read the title for the first time, and they may or may not make sense after you know the story. "A Hard Day's Night" "For Colored Girls Who Have Considered Suicide / When the Rainbow Is Enuf" "They Shoot Horses, Don't They?" "The Unbearable Lightness of Being" "Yellow Submarine" "You Only Live Twice"

It's an idiom. Have you heard of the expression 'eyes wide open'. That is an idiom meaning to see things as they really are. 'Wide open' itself is a descriptive term that means fully open hence what the idiom means. e.g. the door was wide open the windows are wide open his eyes were wide open. Well 'eyes wide shut' is an idiom playing on this, 'shut' having the opposite meaning to 'open'. Refusing to see what is really happening or very strong denial.