Luke has always been impulsive. That has been his character flaw from the start. He acts before he thinks and as he learns his true identity, he doubles down on impulsive decisions because he is a Skywalker and things will always work out because, Force.
A New Hope:
1. Discovers dead Jawas: Runs home to certain death. Lucky stormtroopers have already moved on.
2. On Death Star, learns Leia is on board, mounts rescue mission to detention level despite being told to sit tight.
3. On Death Star, witnesses Obi Wan and Vader's duel. Runs toward it when everyone else is boarding. Screams out to draw Imperial fire.
4. Despite an hour or two of Force training on the Falcon, he decides to abandon technology and use the force to blow up the Death Star. Yes, Obi Wan was prompting him to trust the Force, but it was Luke he interpreted that to mean, "turn off your scanner".
Then comes a major mistake on Obi Wan's part: "Remember, the Force will be with you. Always."
Um? Now Luke just took a major, unnecessary gamble. It paid off. Not because he was lucky, but because some mystical energy has decided Luke is "special". He is chosen. It will guide him.
Empire:
Then he get's impulsive again!
1. Why does he need to investigate a meteor crash in a system full of them? It needlessly put him in harm's way, and by extension, Han and the rest of the Rebels sent out to look for him.
2. On Dagobah, he flashes impatience over and over. Then he goes in the Dark Force cave to face his fears and learns that, yes, he could become the next Vader.
3. He abandons his training to save his friends on Bespin, ignoring his teachers and falling into Vader's trap.
4. Once he loses his friends and comes face-to-face with Vader, rather than disengage and run, he relies on a couple of weeks of training to take on the most feared warrior in the Galaxy.
Considering every misstep Luke makes in this movie, he is lucky to only have lost his hand. But, with Star Wars technology, even that isn't a major loss.
Return of the Jedi.
Time has passed and we are lead to believe Luke has honed his Jedi powers (and by extension his wisdom?). It is no small feat to build a lightsaber, so he likely did have to grow as a Jedi to complete this very dangerous task. Once he is ready to use it, cocky Luke returns.
1. He sends all of his friends into harm's way, planting them strategically in Jabba's Palace before his arrival. He then arrives, used Dark Force powers to choke some Gamorrean guards, and confronts Jabba in a room full of enemies.
2. He tries to use Jedi mind tricks on Jabba and fails, earning a date with the Rancor.
3. He accompanies his friends to Endor, jeopardizing their mission.
4. He turns himself in to the Empire on Endor, confirming to the bad guys that, yes, the Forest Moon has been infiltrated by rebels.
5. The Emperor goads Luke: "Strike me down!" Luke takes the bait, summons his lightsaber, and takes a swing that is interrupted by Vader.
6. He gives into the Dark Side to defeat Vader when he is told they will go after Leia.
7. When the Emperor tells Luke to finish Vader, Luke could have easily turned to face the Emperor with his lightsaber to protect him. Instead, he tosses it away? Wait? What? Why? This leaves him vulnerable to Force lightning. Moron.
Despite all of these missteps, it works out for Luke in the end. He defied orders and logic, yet because he feels he has mastery over the Force, it is okay. It'll work out. He's a Skywalker.
Then he starts a Jedi Academy. As he senses Ben Solo's conflict, the impulsive Luke returns, ready to murder his nephew in cold blood. Luckily, it is a fleeting thought. Unluckily, it is still a fatal mistake. Ben awakens, getting the final nudge to the Dark Side from Luke's betrayal, and destroys the Academy. Not only does Luke have to face the fact that he failed his family, but the dozens of other families that are mourning lost loved ones. For the first time in his life, things are not going to work out for the best. For the first time, he has to face that he is not protected from himself by the Force. His hubris has been shattered, and so has the man. He has to question every move he makes from that point forward because autocorrect is no longer functioning.
So faced with the realization that he has ungodly power and no idea which path is the correct one to take, he makes the only sensible decision he can. "The Force will be with you. Always." What was once a blessing is now a curse. So he exerts his considerable power to close himself off from the Force. He becomes a void in the universe, unable to influence it, but that also means he can't make things any worse. Let the Force get to work balancing the universe. He's out.
Luke had 3 father figures: Obi Wan, Vader, and Yoda. It's been speculated that Obi Wan and Yoda both shut themselves off from the Force when they were in exile, in order to evade the Empire. Only when they are urged back into the fight do they reengage. Luke follows their example, rather than that of his father, who demanded the Force bend to his will. In this, he once again assumes he is choosing the wisest path, the correct path. He is sure of it. It's not cowardly. It's the only option he's allowed for himself to follow.
