From Longman Dictionary of Contemporary Englishignorance is blissignorance is blissWORRIEDused to say that if you do not know about a problem, you cannot worry about it → ignorance
Examples from the Corpus
ignorance is bliss• But then it's probably a case of ignorance is bliss.• Thus, for animals in the absence of suffering, ignorance is bliss.• Truth, therefore, is socially fractious, while ignorance is bliss. 