Star Wars, given its rich history of secondary/EU/Legends body of work has been subjected to many misconceptions, or Myth-conceptions thought the decades. One of the most contentious of years past was the '5 mile fallicy' from West End Games, makers of the first SWRPG. The source books of that game states the 'SSD' class of ships (otherwise known as the Executor class) was only 8 km or 5 miles long, most likely based on a faulty interpretation of the ESB novelisation that mentioned Darth Vader's ship was larger than the five 'ordinary' star destroyers escorting it. Dr. Curtis Saxton later rebuffed this claim and backed up the true size of the ship with canon evidence from ESB itself, showing the length to be 11 miles, or twice as long and 8 times the size per volume. It took a concerted effort on one fan's part to finally change the 'official' word, because many fans and SW 'creators' simply accept any numbers from any number of reference books without thinking or checking if these are supported by the films themselves.
There are many myths in Star Wars that persist even to this day. Sadly Dr. Saxton even perpetuates one himself in the 'Endor Holacaust' myth, forgetting the still active global/planetary shields that protect the moon following the relatively minor destruction of the shield protecting the Death Star. Certainly those shields would be more than enough to protect the moon and the native life from even the large scale debris shone following the explosion of DSII.
Still others are the many myths surrounding TIE fighters and their pilots, and the nature of 'The Academy' that Biggs attended and which Luke hoped one day to join.
I don't intend to cover all these in one post, but here's a little preview:
TIEs do have shields, and this can be demonstrated in ANH where laser blasts explode near TIEs but not on them.
TIEs lacking life support is fully debunked by many sources, the latest of which is the Rebels television series. (I have also speculated that TIE pilots plug their suits directly into the on board life support for more efficient use of power while flying, no need to pressurize the entire cockpit!)
The Academy was a quasi-governmental agency that trained civilian pilots for flying several types of ships, including civil defense force fighters for the various sector/planetary governments, commercial freighters and pilots for hire. Under the Empire the academy increasingly funneled or encouraged many recruits into Imperial service but was never officially an 'imperial' academy. There is just no way Luke would have ever considered going to a school to be a TIE fighter pilot flying for the Emperor.
Does anyone else want to bring to light any other myths that still persist?