Final answer:
Jonas became upset after recognizing the horrifying reality of war which contrasted sharply with the pre-war ideals of heroism and glory, as powerfully illustrated by poets, authors, and artists of the time.
Step-by-step explanation:
Jonas got upset and had an outburst because he knew what war was really like. The revelations of war's brutality could be overwhelming as witnessed by personal accounts and depictions. Poets like Wilfred Owen and Siegfried Sassoon, and authors such as Erich Maria Remarque and Ernest Hemingway, depicted the inhumanity and senselessness of conflict, often countering romanticized notions of glory that many held before experiencing the front lines. World War I's legacy included profound psychological impact on soldiers and the peeling away of illusions about military heroics, as the grim reality of trench warfare, the absurdities of command strategies, and the heavy toll on physical and mental health became evident. This shift in perception was also reflected in the visual arts, through artists like Käthe Kollwitz, who conveyed the deep personal suffering and mourning caused by the war.