must可以表示“偏偏,偏要”,指不愉快的事

After I gave her my advice, she must go and do the opposite.我给她出了主意后她偏反着干｡

Just when I was going out, someone must knock at the door.我正要外出,偏偏有人敲门｡

Must you trouble him, just when he is busy doing the cooking?他在做饭,你干吗偏要打扰他 ?

Though she didn’t need to, she must go.虽然她不用去,她却偏要去｡

You don’t have to come again, but you must.你不必再来,可是你执意要来｡