Yes, Thucy, I totally get what the poem is saying, and have thought about the poem quite a bit over the years.
But Barrie is right. You can't. You can try, but you're not really human if you march on, head unbowed, after your five-year-old daughter has died.
We don't control what events happen to us and those we love, and we fully control our response to it only if we can become sufficiently detached, which is far from a noble goal. Give me instead Sir Andrew Barton:
"'Fight on, my men,' says Sir Andrew Barton,
'I am hurt, but I am not slain;
I'll lay me down and bleed a while,
And then I'll rise and fight again.' "
" Do you not see how this poem is a triumph over his grief and disability....?"
Do you think this line is actually true?
"In the fell clutch of circumstance
I have not winced nor cried aloud."
Do you think, if it were true, it would even be admirable?