Comment by vladms

I would claim there is no 100%. At least in engineering my professors were saying (paraphrasing) that it's all about trade-offs and most of the times there is not "one answer". I think many education systems (up to graduate at least) instill the idea that there is always "one answer" which has many bad repercussions later (people seeing things in black and white).

I don't think a student needs to always answer a question "on the spot". Being able to find an answer in a reasonable amount of time and explain an answer would be in my opinion more valuable. So then it's more about "how efficient can the student give the answer to the question" (answer on the spot, spend one hour, spend one week, etc.).