Wiktionary
a. (context idiomatic English) strong and determined (qualifier: especially more so than someone else, to whom one is being compared).
Usage examples of "made of sterner stuff".
What if she's made of sterner stuff than Davits, who used to hunt sharks with poison-darted air pistols?
Your Frodo is made of sterner stuff than I had guessed, though Gandalf hinted that it might prove so.
One of the wizards whimpered, but the Carnadosan priest who'd tried to kill Zarantha was made of sterner stuff.
One of the wizards whimpered, but the Carnadosan priest whod tried to kill Zarantha was made of sterner stuff.
The God King in command of that oolt not only had more warning but was made of sterner stuff as well.
Jeyne covered her eyes whenever a man fell, like a frightened little girl, but Sansa was made of sterner stuff.
If I'd been alone, I might have panicked and bolted, but Kurda and Gavner were made of sterner stuff, and their calm presence held me in check.
My father, and most of the others in Amber and the Courts, swear by the heavy, awkward things, but they are probably made of sterner stuff than myself.
Having been in love on several occasions, most notably with the director's great-grandmother, I insist that obsession should be made of sterner stuff.