The domino effect. The greenhouse effect. The Graham Norton Effect. We live in a world of action and reaction, where simple operations lead to complex outcomes. No human endeavor is exclusive to the laws of nature, not even cinema. As with compounds, movies are defined by a combination of elements. Change one thing, and you have a completely different movie. A choice of direction, a casting decision, or a simple joke can all affect a film's legacy. Just ask the internet.
The internet is credited with all manner of social phenomena, from uprisings to addictions. What it's best at, though, is pointing out the flaws in movies. Like monkeys combing for insects, the wired generation can find something wrong with any movie, even a good one. It's a natural extension of our desire to understand how things work. The danger lies in losing our ability to enjoy anything without picking it apart.
The movies on this list were all successful. Some were beloved upon release, but have since lost their lustre. Others made tons of money despite the massive amounts of nerd rage they engendered. One way or another, a modest tweak could have made them all significantly better.