Pedantry and mastery are opposite attitudes towards 
rules.
1.  To apply a rule to the letter, rigidly, unquestion-
ingly, in cases where it fits and in cases where it does not
fit, is pedantry. Some pedants are poor fools; they never
did understand the rule which they apply so conscientiously
and so indiscriminately. Some pedants are quite
successful; they understood their rule, at least in the 
beginning(Before they became pedants), and chose a 
good one that fits in many cases and fails only occasion-
ally.
     To apply a rule with natural ease, with judgement,
noticing the cases where it fits, and without ever letting
the words of the rule where it fits, and without ever letting
the words of the rule obscure the purpose of the action
or the opportunities of the situation, is mastery.
     2. The questions and suggestions of our list may be
helpful both to problem-solvers and to teachers. But
first, they must be understood, their proper use must be
learned, and learned by trial and error, by failure and
success, by experience in aplying them. Second, their
use should never become pedantic. You should ask no
question, make no suggestion, indiscriminately, follow
following some rigid habit.  Be prepared for various question
and suggestions and use your judgement.  You are doing
a hard and exciting problem; the step you are going to
try next should be prompted by an attentive and open-
minded consideration of the problem before you. You
wish to help a student; what you say to your student
should proceed from a sympathetic understanding of his
difficulties.
     And if you are inclined to be a pedant and must rely
upon some rule learn this one: Always use your own
brains first.