The Cask of Amontillado

Reading the story "Cask of Amontillado" by the great Edgar Allan Poe, I wasn't able to understand anything. (Even if I read it alongside my beloved dictionary for the nth time!) The words were too much too handle. I was able to visualize some parts but they weren't that clear. But when we watched the short film of this story, I realized that even the blur parts that I visualized weren't even part of the story at all, I guess I had the wrong interpretation. Seeing the movie, I was shocked thinking that any man can be this cruel. It's really scary thinking that even the person beside you may have the biggest grudge on you without you knowing.
At the same time of all this paranoia I am expressing, it also makes me wonder that why no one at present ever thought of doing the same thing as what Montressor did (or maybe close to what he did). Planning of what we may call a "perfect murder", aren't they (those criminals) wise enough to think so or did Montressor just had a grudge that seeks the best of the best revenge? If so, what made him tick-off knowing that Montressor was a very patient friend of Fortunato.