In the original Star Wars movies (pre-Special Edition), Han Solo has a conversation in the cantina with a bounty hunter named Greedo. Greedo wants to take Han Solo in for a bounty, and Han Solo disagrees with him by shooting him from under the table.
In the Special Edition, Lucas decided he didn’t like Han being that much of a rogue, so he had Greedo shoot first, missing Han from a whole four feet away, with Han shooting him immediately afterwards. It was fixing (poorly) something that wasn’t broken in the slightest to begin with.