"Man can be destroyed but not defeated." How is this exemplified in The Old Man and the Sea?

The idea that man can be destroyed but not defeated from
The Old Man and the Sea could be explained or paraphrased
as:

• A man can be killed, but as long as he
  doesn't quit he can't really be
  defeated.

Santiago goes fishing day after day
even though he is on a "losing streak," as we might say today.  He hasn't caught a fish
for a very long time.  He survives only because the boy brings him bits of food.  But he
doesn't quit.  He continues to fish everyday and continues to try.  His "spirit" is not
broken.

More specifically, Santiago hooks the marlin and
does terrible battle with it.  He is an old man but he uses his strength and wits to
defeat the fish, at the cost of great physical suffering.  Again, he doesn't quit.  Even
after he defeats the marlin and then must fight the sharks, he continues the battle. 
His spirit remains strong.  He doesn't get the fish home in the kind of shape he needed
to earn money for it--he fails, technically.  But a man who keeps fighting is not a
failure. 

This is Hemingway's modern view on the warrior. 
Hemingway is too modern and worldly and intelligent to pull the old cliche of the
warrior giving it all he can and being unrealistically victorious.  The "good" or
"right" or "just" doesn't always win.  The knight in shining armor doesn't always carry
the day.  But Santiago can fight, nevertheless.  This makes him noble, like the marlin. 
And it makes him undefeated.