Carl M. Tomlinson said this quote

“ A circular plot structure, often seen in adventure novels and quest fantasies, is a narrative devise involving setting, character, and theme. Typically a protagonist ventures from home (or the starting place of the story), goes on a journey, often a dangerous one in which many challenges are overcome, and then returns home a changed person. The plot is usually chronological, with the events occurring in a setting that becomes a circle. By returning the character to the place where he started, the author can emphasize the character’s growth or change while also highlighting the theme of the story. ”