How is being hit by a hard word
 different from being hit by 
  a brick or a bat?

To burn, the spark of a hard word
  must find some kindling inside
   the recipient, elsewise it can't ignite. 

If someone points at me and screams:

"YOU ARE SUBPAR AT ALGEBRA!"

I remain unwounded.

[I'd like to say that it doesn't burn
  simply because it's true, 
   but the truth or falsity of hard words 
   is -- perhaps sadly -- not a major
   ignition factor.

 The kindling is a thing that sits inside one --
  something that makes one care,
   probably a complex mélange of factors.

 The truth of hard words? 
   That is an outside factor.]

Even if I were to discover that,
  to the person who issued the insult,
   there is no greater disparagement 
   than to cast aspersions upon a 
   person's middle school-level
   mathematics competency, 

I would remain unwounded. 

If I were to feel any sort of way
  about uncovering that knowledge,
   it would be to feel sort of bad 
   for the person who issued the taunt.

Now, how to burnproof one's soul,
  that is the question?