Very often things like flashbacks, flash forwards, non-linear narratives, multiple plots and ensemble casts are regarded as optional gimmicks stuck into the conventional three act structure.
Explanation:
More than six ways to turn your idea into a film. Let's imagine that you've read a newspaper article about soldiers contracting a respiratory disease from handling a certain kind of weaponry. You want to write a film about it. Conventional wisdom says create one storyline with one protagonist (a soldier who gets the disease) and follow that protagonist through a three act linear journey. There's no question that you could make a fine film out of that. But there are several other ways to make a story out of the idea, and several different messages that you could transmit - by using one of the parallel narrative forms.
