Kitāb al-Ghayba > Concealed Birth of the Imam of the Time (a.s) was not an extraordinary event
Hadith #13

وقد كان من غيبة موسى بن عمران عليه السلام من وطنه وهربه من فرعون ورهطه ما نطق به القرآن ولم يظفر به أحد مدة من الزمان ولا عرفه بعينه حتى بعثه الله نبيا ودعا إليه فعرفه الولي والعدو.

There is the story of the hiding of Musa, the son of Imran from his homeland and his flight from Firon and his people, as mentioned by Quran. No one found him for a long time, neither did they recognize him, until God sent him as an apostle and he made the call to follow him and then the friend and the foe recognized him.