Not necessarily true. Every clown is different and have their own personality. It's true that it's not always the best idea to add clowns separately but that's because of territorial reasons. The reason people may say it's 'harder' to pair them is just because it takes longer to pair if they even pair at all. If you buy 2 clowns that are already paired or at least from the same batch at the LFS, well the ground work is already done. If you walk into a bar with someone you're seeing, after a few beers you already know what's going to go down afterwards. But walk in solo and expect the same outcome, well that is going to take some time and ground work... maybe even a few more beers.