The idiom 咎由自取 is formed through a literal composition of its four characters: 咎 (blame), 由 (from), 自 (self), and 取 (to take). These characters are arranged in a direct sequence where 咎 serves as the result, 由 indicates origin, 自 identifies the agent, and 取 specifies the action, collectively yielding the meaning that blame or misfortune is brought upon by one's own actions.