It's because first everyone's very well mannered. No one really expects anything to happen.
Zuerst benimmt man sich und
erwartet nichts Wildes.
Ew. Your stepmother expects you to be at your half-brother's party when your full father gets here.
Deine Stiefmutter
erwartet dich bei deinem Halbbruder, wenn dein Vollvater kommt.