Motorcyclists, mountain bikers, pilots, all worry about target fixation, a phenomenon in which you focus so intently on a hazard you want to avoid that you slam into it, in a kind of self-fulfilling prophecy of the senses.*
This is how we're wired. It saves us energy, mental storage space, and time. Neuroscientists call this "predictive coding," a kind of ongoing unconscious educated guessing of the senses. We constantly and pre-consciously make assumptions about the world, and these assumptions are embedded in perception. Perception is selective; we see by anticipating what we'll see based on our past experience; we see what we expect to see.
The eye and brain are not really separate as we presume; the model of the receptor and the processor is not entirely accurate. According to recent studies our primary visual cortex is influenced from above motivations, predictions, and assumptions in higher centers of the brain. Visual channels seem to flow both ways, both receptive and informing. Researcher Ramesh Jain has called perception a "controlled hallucination" in which sensory input is a means of confirming and adjusting expectations rather than a wholesale intake of stimuli.
Seeing is a process of continuous predicting, visualizing, and hypothesizing. It is not difficult to imagine this process continuing without external sensory stimuli in the form of dreaming and imagination. In the art teaching world, we often see "drawing from life" and "working from your imagination" as somehow opposed, or at least springing from very different sources; yet perception and imagination are informed by some fundamental process of continuous visualization. You create your own world. I often had this feeling, after working very hard on my art, that the world looked like my art. I was creating my art, and creating through my art a way to see world.
When we see, our expectations are almost always confirmed (optical illusions take advantage of figures and diagrams that confound expectation, and we sometimes mistake one person for another, or drive off the highway when we wrongly assume a bend in the road). We create our own reality, perceptually, and ultimately we create our own outcomes based on those perceptions. Expectation is embedded in perception; perception becomes reality.
It's as if we can predict the future; we are actually making it happen. The world we perceive is a dream that almost always comes true.
*(Another side of target fixation -- I was learning archery, and the best book on the subject told you to pretty much forget about your stance, your form, and your equipment and just fixate on the target until everything around you disappeared. It worked).