[header] How to forget something horrible you saw on the internet [title] Use thought substitution to overwrite the horrible image. [step] The idea behind thought substitution (sometimes called thought displacement) is that you have the ability to control what you think and how you react. You can intentionally forget bad memories by filling your mind with more positive things. 
Your brain has a limited focus, and you can only keep so many thoughts in your immediate sphere of awareness. Try to replace the negative memory by exposing your brain to something brighter.