Flashforwards occur when scenes portraying events that occur at a point in the future are edited to precede the scenes depicting events leading up to that point. An extreme example of flashforwarding is the back-to-front organisation of scenes in Christopher Nolan's Memento. Every scene in this film is effectively a flashforward because the events in each scene occur immediately before the events in the preceding scene. The film starts with the final scene and ends with the first scene, so the story effectively unravels backwards. This is not a typical method of portraying time at all, but it is highly effective in Memento since the lead character has no short-term memory. Therefore, by showing the scenes backwards, the filmmakers ensure that the audience, like the lead character, have no idea what events have occurred prior to any given moment.

How is this related to flashforwarding? Why does short-term memory need reversing time? Is it to remind him or her what happened recently to compensate for his lack of short-term memory?
no short-term memory.