People believe that what they see is real.
The proverb has been traced back to 1609 and it was cited in an unpublished manuscript in the library of Trinity College, Cambridge. First attested in the United States in the 1732 Jonathan Belcher Papers. According to this old maxim, you can in fact believe your eyes. See also Believe only half of what you see and nothing that you hear. People believe that what they see is real.