The detail, which demonstrates the central idea that Seo-Jun is less diligent than his mother, when she was young is this: SEO-JUN ENJOYS SPENDING TIME WITH HIS FRIENDS.
Friends are central to the life of Seo-Jun, he likes making friends and he loves spending time with them. This leaves him with less room to do effectively those tasks that are expected of him. When his mother was his age, she was a very diligent young woman, who did not spend time on frivolities, such as spending much time with friends.
