Be made of sterner stuff
Definition 1 of 1
Pro Tip 1/3Emotional Grit
This phrase often implies emotional strength as well as physical or mental resilience. 
Her unwavering optimism during the crisis showed she was made of sterner stuff.
Pro Tip 2/3Unexpected Tenacity
Used when someone's resilience is surprising or exceeds what's typical in a given situation. 
Despite his quiet demeanor, he proved to be made of sterner stuff.
Pro Tip 3/3Figurative Expression
The phrase is metaphorical and not about physical substance but personal qualities. 
Even the harshest criticism didn't faze her; she's made of sterner stuff.