A quite ill patient is examined by a physician. After examining the patient,
the physician realizes that she/he has never encountered this set of
symptoms before, or at least she/he doesn’t remember having
encountered them.  Imagine the physician giving one of these responses
to the patient:

1.  “Sorry, I can’t help you. I can’t find the answer in my textbook.”

2.  “Sorry, I can’t help you. There is something wrong with your blood
chemistry, but I can’t remember what I learned in first-year chemistry.”

3.  “Sorry, I can’t help you. I wasn’t told about symptoms like yours
in medical school.”

Clearly, physicians or scientists cannot be familiar with every case, or
remember all the information they learned in their training. But by learning
how to approach complex problems, they are equipped to deal with cases
for which they have been trained, and more importantly, are able to deal
with new issues. Therefore, they must know how to approach complex
problems by disaggregating them into simpler steps.