Luke attended a briefing in which he and other pilots were told that if they could shoot a proton torpedo into a specific exhaust port, it would travel down a reactor shaft, (bending through all the twists and turns of the shaft without prematurely detonating) and would reach the station's core and start a chain reaction which would destroy the Death Star and save Yavin and the Rebel Base.
Luke was piloting an X-Wing Fighter for the first time in his life. He was in combat for the first time in his life. His best friend was just killed in the battle trying to protect him. All the while a ghost kept telling him to turn off his targeting computer. This seemed to make sense to Luke, so he did. Alliance Command immediately questioned why the pilot with whom the entire Rebellion's survival rested decided to turn of the computer. He told them not to worry, so they didn't. With the terrifying Dark Lord of the Sith bearing down on Luke, Han Solo appeared out of freakin' nowhere and shot up Vader's wingmen, forcing him out of the trench, and freeing Luke to take a shot. He fired his torpedos when it felt right.
Luckily for the Alliance, the exhaust port had just been accidentally switched from blow to suck by a drunk Wullf Yularen (who was spending too much time thinking about how he went from being an Admiral to a Colonel) only seconds after Red Leader Garven Dreis's torpedo shot was blown off course by the rush of outgoing air. This caused Luke's torpedos to be sucked right down the tubes into the heart of the station. Later, after inspecting the Death Star Plans more closely, Rebel military analysts determined that the proton torpedos would actually have been sucked into the Arby's in Sector 14, and done little damage. However, the torpedos deflected off the bottom of the controversial hi def video screen hanging from the roof of Admiral Motti's recently completed football stadium, and bounced straight into the reactor core.Luke decided to get the hell out of there, and survived the resulting cataclysmic explosion along with Wedge Antilles, Han Solo, Chewbacca, and some dude name Keyan Farlander that nobody really cared about until they made an action figure of him. Other pilots survived, but they didn't get much recognition. They weren't happy about it, but at least they weren't banging their own sisters.