Georg Miller did some research on memory and discovered that an average human can remember about 7 plus/minus 2 items in his working memory.
When creating solutions UX Designers should always keep this law in mind. How should a user choose an option if the user has already forgotten the first one after reading the last one? Therefore every designer should always offer a maximum 7 plus/minus 2 elements. Today there are many designers and psychologists that say the numbers should be adjusted to 5 plus/minus 2.