Sequels are natural launching pads for flashbacks and flash-forwards. What better time for a character to let his mind relive a significant past event (a flashback) than when he is thinking about his current predicament? Here's an example of a flashback situation:  

A teenager has just encountered an obstacle that frustrates his plans to attain a goal. He reacts emotionally to the event and begins to review the circumstances that led up to it. He may enter the phase of analysis, where he considers his current situation. He sees no way forward, and in his discouragement he is reminded of some significant event in his past. His mind slips into a vivid, in-the-moment reenactment of that event (a flashback). After the character's mind returns to the present, he realizes that reliving event has provided him with insight that shows him a way out of his current predicament.

When a character is considering a potential new course of action, what better time for him to slip into a flashforward where he imagines that course or its outcome in detail as if it were already reality. For example:

A character is well into a sequel, and he has narrowed his potential courses of action to one. As he hesitates before making the decision, he visualizes his course of action vividly as it is happening (a flashforward). He may even imagine in detail, his euphoria, acts of celebration, and the congratulatory remarks of others. After the character's mind returns to the present, he makes his decision with greater confidence.

A flashforward provides an opportunity to dramatize a scene that won't materialize in the real time of the story. The character and the reader get the benefit of experiencing the scene, but the course of action eventually fails to happen as visualized, and the character's hopes are dashed again.  

Examples of flashbacks in popular fiction abound. For example, Hatchet, by Gary Paulsen, has many flashbacks as the protagonist relives the events related to his parents' divorce. Flashforwards are not so common, but John Grisham uses one in The Client (paperback edition, 262-265) where an attorney imagines the harsh treatment that may be in store for her young client. Her guidance helps the boy avoid the situation she imagined. The next time you notice a flashback or a flashforward in published fiction, take note whether the character is engaged in reflection, quite probably after an emotional experience, i.e., in a sequel.