This is a psychological pricing approach that is aimed at making customers prefer one product over another. The effect is achieved by offering them a choice of at least three items, where one is cheap and has a low value, another (the key product) is expensive and highly valuable, and the third one (the decoy) is only slightly cheaper than the promoted item but has discernibly fewer benefits, so customers see no point in buying it. They would rather pay a little bit extra and enjoy the most valuable product – it seems like a rational choice.