11. A system comprising: a processor; and a memory storing instructions that, when executed, cause the system to: determine an inferred interest for a first user; generate a model based on the inferred interest of the first user and store the model in the memory; generate a set of candidate content items using an item from a second user with a similarity to the first user; determine a first attribute and a second attribute associated with a candidate content item in the set of candidate content items; determine a first score associated with the first attribute for the candidate content item based on the model of the first user and a first number of candidate content items having the first attribute in the set of candidate content items; determine a second score associated with the second attribute for the candidate content item based on the model of the first user and a second number of candidate content items having the second attribute in the set of candidate content items; compute a third score for the candidate content item in the set of candidate content items by summing the first score associated with the first attribute and the second score associated with the second attribute; select content items for a stream of content associated with the first user from the set of candidate content items based on the third score of the content items; generate an explanation for a first content item in the selected content items, the explanation indicating a reason for presenting the first content item to the first user; and transmit an instruction to a device that causes the device to present for display the stream of content to the first user with the explanation alongside the first content item, the explanation including a selectable graphic element for the first user to access an expanded explanation.
11. A system comprising: a processor; and a memory storing instructions that, when executed, cause the system to: determine an inferred interest for a first user; generate a model based on the inferred interest of the first user and store the model in the memory; generate a set of candidate content items using an item from a second user with a similarity to the first user; determine a first attribute and a second attribute associated with a candidate content item in the set of candidate content items; determine a first score associated with the first attribute for the candidate content item based on the model of the first user and a first number of candidate content items having the first attribute in the set of candidate content items; determine a second score associated with the second attribute for the candidate content item based on the model of the first user and a second number of candidate content items having the second attribute in the set of candidate content items; compute a third score for the candidate content item in the set of candidate content items by summing the first score associated with the first attribute and the second score associated with the second attribute; select content items for a stream of content associated with the first user from the set of candidate content items based on the third score of the content items; generate an explanation for a first content item in the selected content items, the explanation indicating a reason for presenting the first content item to the first user; and transmit an instruction to a device that causes the device to present for display the stream of content to the first user with the explanation alongside the first content item, the explanation including a selectable graphic element for the first user to access an expanded explanation. 12. The system of claim 11 , wherein the memory also stores instructions that, when executed, cause the system to distribute the stream of content in a social network; and share at least one selected content item with a friend of the first user.