Don't remember exactly which interview or databook I read it from, but the wikia has a decent paraphrasing of it.
Although Sakura is the most recurring female character in Naruto, Masashi Kishimoto did not originally intend for Sakura to be the heroine of the series, even stating on occasion that he still has a hard time viewing her as a heroine. Kishimoto attributes this to him being unable to draw good heroine characters, and fashioned Sakura as a girl who cannot understand men, the best example of a heroine he could come up with. Sakura's creation is a result of Kishimoto's desire to make a somewhat irritating character who was well-intentioned.