Warning! SPOILERS for Star Wars episode 28 are present in this post. Luke Skywalker mistakenly predicts the future in the most recent issue of Marvel's Star Wars comic book series, in which he will accidentally draw his lightsaber on Ben Solo during a moment of weakness, sending him into Snoke's arms and forging a terrible warrior for the dark side.
After the events of Empire Strikes Back, Marvel's Star Wars comic book series describes the Rebellion's battles with the Empire prior to Return of the Jedi. Luke Skywalker's rapid rise to power between Empire Strikes Back and Return of the Jedi has always been a mystery, but these comics are filling in the blanks and giving the much-needed context on Luke's ascent to the rank of Jedi Knight.
Luke Skywalker infiltrates Coruscant, the Emperor's home and a stronghold for all things Imperial, while posing as an Imperial officer in Charles Soule and Andrés Genolet's Star Wars #28. Luke makes the decision not to use his lightsaber, claiming that he would "be tempted to use it if I had it." Luke takes the wise choice to forego his lightsaber in a scenario where doing so would be counterproductive since he anticipates that if pressured, he will reach for it even if he doesn't necessarily need to use it. Sadly, Luke later showed poor judgement when he brandished his lightsaber at Ben Solo, as was depicted in The Last Jedi.
Luke understood that having a gun was tempting.
Luke, a novice Jedi with much to learn, had the wisdom to eliminate a choice before the moment when he would be most tempted. Years later, if only Luke had taken his own advice, their relationship would still be intact today. If Luke had listened to his previous self, a single error of judgement that altered the course of the entire galaxy could have been completely prevented. Not that Luke is aware that any Jedi might draw their sword in a time of need, but rather that he is aware that the best course of action in some circumstances is to disarm oneself, is telling. While it's questionable whether Luke Skywalker should take responsibility for momentarily lighting his sword after detecting Ben Solo's gloom, this action demonstrates that he is aware of the danger of having his blade so close at hand. Given how prudent the choice is at this stage in his life and how clearly it detects and avoids the worst in human nature, it is rather surprising that he didn't include this lesson in the training he provided Padawans later in life.
Luke Skywalker was prone to errors even in his advanced age and with his years of Jedi training and expertise under his belt. Ironically, a younger Luke, who had less life experience, would have been stricter and safer with his lightsaber and how discreetly he would use it. Between this Marvel Star Wars story and Luke taking on the responsibility of training Ben, there is still a significant amount of time, and not even the great Luke Skywalker is immune to the horrors of Imperial war. He is not the man he will eventually become; he is a man of great self-control and constraint right now. Because fans now know that Luke Skywalker foresaw even he would be tempted to use his lightsaber in the wrong situation, but forgot that lesson in the moment when it was most important to remember, Ben Solo's reaction to Luke Skywalker brandishing his lightsaber against him will forever remain a great "what if" in Star Wars history.