The idea behind "The Blind Men and the Elephant" is based upon the principal that our perceptions are founded on the information that we are able to accumulate. In the story, each man touches a different part of an elephant, and based solely on these individual perceptions (from only the sense of touch), each man has a different idea about the shape of the elephant. However, his knowledge is limited and inaccurate, for it is the result of partial knowledge, not the entire "picture."
Literally, we can see how this might be translated into a real-life experience. If someone lives a humble existence somewhere in the world, cut off from the news and pictures of the "world outside," that person might be content with the circumstances of his life, not worried about what exists elsewhere. However, if another person living in that same community has a visitor who brings a newspaper or some kind of electronic device (a phone with pictures, etc.), the second person's mind will be opened to things he or she never imagined in the world. Life on the outside of this village presents a far larger world than the second person had ever considered. Where the first person may be content in his limited exposure to the world, the second person will see his own world most likely with less satisfaction and the larger world with greater curiosity.
In this case, "perception" is purely relative—to what we know—and what we have experienced. If someone believes in ghosts, a bump in the night may be terrifying; but if someone else does not, he or she will explain it away to the sounds of an old house settling. The truth for each person is relative to his own experiences, and therefore, each person's perception will be different (in a large or small way) based upon the collective experiences and/or knowledge each person has.
Each of us perceives the world relative to our own knowledge. We need not be blind to have different perceptions from others—it is all relative to what we have experienced in our lives.
"The Blind Men and the Elephant" shows that reality is relative to one's perception. The blind men, having been able to access by touch (which is their substitute for vision) different parts of the elephant, each had different perceptions as to what the creature looks like. Now, no one could say that their individual (and differing) ideas of what an elephant looks like are wrong; at least to a localized area their perception would prove accurate. Thus for them, an elephant in their individual "realities" are different; and this is due directly to their differing perceptions.