Convoluted flashback structures are not only intellectually based, they tend to distance the viewer from that 'simple reality' they come to the movies to enjoy. It is no surprise that many great movies with complicated or innovative flashback structures were not particularly popular, not crowd-pleasers. (DVDTalk.com)

It is true that flashbacks can make the majority of the story confusing, but the concept is a bit like putting a puzzle together - you're not really sure where each piece fits or what the picture really looks like until the very end. Therein lies the payoff. (streetdirectory.com)

The flashback should be prompted by an incident, dialog, or intense action which brings a vivid memory to the character. (Helium.com)