Of all the supposed errors in Star Wars it seems to be the one that people have spent the most time trying to fix. When Luke and Obi-Wan first meet Han Solo in A New Hope, he brags about how fast The Millennium Falcon is by saying it completed the Kessel Run in “less than 12 parsecs.” This seemingly simple line of dialogue has caused a surprising amount of strife, because a parsec is a measurement of distance, not speed meaning that Han’s statement makes no sense. While it would be easy to dismiss the apparent error as a situation where George Lucas simply tried to use “futuristic space” sounding language and ended up making a grammatical error, there have been plenty of people trying to come up with a different explanation.
One of the simplest explanations is that Han was lying. Han is a character who would sometimes make things up as he went along without any real plan. We even get to see a little bit of that later in the movie when he tries to convince an Imperial officer that everything is fine and normal in the detention block. So it wouldn’t be crazy to assume that Han is simply making up facts on the fly about how good his ship is and used the wrong word in lying. There is some evidence to suggest this is true. In an early draft of the screenplay for the movie, after the line about the Kessel Run, there is an action line that describes Obi-Wan as making a face, suggesting that he doesn’t buy what Han is saying. Even in a later version of the script, there is a parenthetical attached to the line to indicate that Han is “obviously lying” when he says that his ship completed the Kessel Run in less than twelve parsecs.
However, regardless of what the script said, in the final movie, Han seemed to be pretty earnest when talking about the ship, and neither Obi-Wan or Luke seem to take issue with him using the term parsecs, so many fans weren’t satisfied with the lying angle. On top of that, when the record is brought up again in The Force Awakens and Rey mistakenly says that the Millennium Falcon did the Kessel run in fourteen parsecs, Han is quick to correct the number, suggesting that the claim wasn’t something made up on the spot.
In the commentary for the DVD release of A New Hope, George Lucas offers an alternative explanation. Lucas explains that Han Solo’s boast in the movie has less to do with the speed of the ship, and rather is bragging about how good the ship’s computer is. According to Lucas the Millennium Falcon’s advanced navigational computer is able to calculate much faster routes than other ships. Meaning that the Falcon was able to find a shorter and thereby faster path from point A to point B in the Kessel Run. This idea is seemingly backed up in a document from 1977, when Lucas began to put together a knowledge database of Star Wars in preparation for the expansion of the franchise beyond the first movie. When describing the Millennium Falcon, the ship is described as simple and economical, but modifications to the ship are extensive including to its navigational system.
The idea was further expanded upon in A.C. Crispin’s Han Solo trilogy of books, when the Kessel Run was expanded upon in greater detail. It turns out that the Kessel Run was a specific 20 parsec long smuggling route that was close to a cluster of black holes known as The Maw. Han’s famous Kessel Run involved Han flying closer to the black holes than other pilots would be comfortable with, thus cutting eight parsecs off of the standard run time. While this was part of the Legends timeline that was deemed non-canon after the Disney acquisition, this explanation was more or less reintroduced as the official explanation of the line in Solo: A Star Wars Story, when Han does successfully fly the Kessel Run, using what he describes in the movie as “A shortcut.”
Of course, even in that movie, when Han brags that he pulled off the run in less than 12 parsecs, Chewbacca pushes back against the claim, causing Han to clarify that he was rounding down to be able to make the claim. So maybe in the end, Han was lying after all.