There is no right answer

Learning happens by comparing, contrasting and assimilation & composition.

When we make a learning, there is no right answer. Learning happens via matching, filling in the blank and question & answering.

Sometimes neither the question remains correct nor the answer remains correct. 

When Question is incorrect, there is no requirement to answer or figure out question from answers and provide best match.

When answer is incorrect, there is no requirement to answer or figure out best match answer for the questions.

Hard Problem don't generally have a well defined question and a well defined answer. They are computationally complex and not comprehensible both for our brain and automatas.