The Butterfly Effect (2004)

Evan Treborn (Ashton Kutcher) has lost track of time. From an early age, crucial moments of his life have disappeared into a black hole of forgetting, his boyhood marred by a series of terrifying events he can't remember. What remains is the ghost of memory and the broken lives of his childhood friends, Kayleigh (Amy Smart), Lenny (Elden Henson) and Tommy (William Lee Scott). Throughout his childhood, Evan was under the care of a psychologist who encouraged him to keep a journal, detailing the events of his day-to-day life. Now in college, Evan reads from one of those journals and finds himself thrust inexplicably back in time. Evan comes to realize the notebooks he keeps under his bed are a vehicle, a way to return to the past to reclaim his memories. But these recollections only leave Evan feeling responsible for the damaged lives of his friends, especially Kayleigh, the childhood sweetheart he still loves. Determined to do something now that he was incapable of doing then, Evan purposely travels back in time, his present-day mind occupying his childhood body, in an attempt to re-write history and spare his friends and loved ones these traumatic experiences. By altering the events of the past, Evan hopes to transform the present. But every time Evan changes something in the past, he returns to the present to find his actions have unexpected and disastrous consequences. Try as he might, he can't seem to create a reality that allows he and Kayleigh to live "happily ever after."