TNG Season 6 Episode 15: Tapestry

Picard is dead. Q is God. The universe, fortunately, is not that badly designed. Q gives Jean-Luc the option to go back and fix what ails him (his reliance on an artificial heart) by avoiding his injury at the hands of a burley Nausicaan in the first place. Unfortunately it turns out that the result would be a very different man.
Okay, so this one is basically the Next Generation version of It’s A Wonderful Life, but it also has Q to recommend it, as well as the fact that you learn more about Jean-Luc’s youth and why he laughed when he was stabbed through the back and heart.

Plot

During a diplomatic mission, Captain Picard is rushed to sickbay due to severe, unexpected injuries. After dying from his wounds, he awakes to find himself in an otherworldly realm, where he is greeted by the god-like alien Q. Q greets him with, "Welcome to the afterlife, Jean-Luc — you're dead!" Q explains that the energy weapon that shot Picard destroyed his artificial heart, and that a natural heart would have survived the shot. Picard lost his original heart as a young officer, when he was stabbed during a bar brawl, an event he regrets. When Picard remarks that he would do things differently if he could relive that moment, Q sends Picard back in time to two days before the brawl, where he meets with fellow cadets and friends Corey Zweller and Marta Batanides. They are surprised by Picard's change of personality; no more devil-may-care attitude.
Zweller is cheated by a Nausicaan at a bar game, and plans his revenge trying to rig the next match, but is prevented from rigging the table by Picard. When the Nausicaans try to bring Zweller into another game, Picard prevents it. When Zweller is goaded into attacking the Nausicaans after being called a coward, Picard intervenes by holding Zweller back, averting tragedy but humiliating his friend. Zweller leaves him in disgust. Marta is attracted by Picard's unexpectedly mature behavior and has a one-night stand with him, but it complicates their friendship.
Q returns Picard to the Enterprise in the present. Instead of being the captain, Picard is a junior science officer who has led an unremarkable career doing routine work. Picard consults Commander Riker and Counselor Troi (Q having promised only Picard's future would be changed by his past actions), who explain that his aversion to risk means he has never distinguished himself.
Picard confronts Q, who tells him that although the fight with the Nausicaan nearly cost him his life, it also gave him a sense of his mortality. It taught him that life was too precious to squander by playing it safe. Picard realizes that his attempts to suppress and ignore the consequences of his indiscretions have resulted in him losing a part of himself. Picard declares that he would rather die as the captain of the Enterprise than live as a nobody. Q sends him back to the bar fight and events unfold as they did originally, with Picard being stabbed through the heart and laughing as he collapses to the floor.
Picard awakens in sickbay, captain of the Enterprise again. As Picard recovers from his injury, he wonders whether his journey into the past was one of Q's illusions or merely a dream. Regardless, he is grateful for the insight the experience gave him.