ignorance       
noun [ U ] uk/ˈɪɡ.nər.əns/ us/ˈɪɡ.nɚ.əns/
C2 无知,愚昧
lack of knowledge, understanding, or information about something
  Public ignorance about the disease is still a cause for concern. 公众对这一疾病的无知仍是一个令人担忧的问题。 
 Patients, it is claimed, were kept/left in ignorance of what was wrong with them. 据称,病人对于自己得了什么病还被蒙在鼓里。 
 Idiom  
ignorance is blissidiom  saying 无知便是福
said to emphasize that sometimes it is better for you if you do not know all the facts about a situation