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Every second, your eyes collect millions of pieces of visual information. If your brain kept every single detail, you'd quickly become overwhelmed. Instead, it automatically filters out most of what it considers unimportant and keeps only the information it thinks you'll need.
This is why you can walk into a room and completely miss an obvious object that's right in front of you. It's also the reason magicians can perform tricks in plain sight. Your brain isn't showing you everything—it shows you what it believes matters most.
© National Institutes of Health