harden one's heart

harden (one's) heart

To stop or cause one to stop feeling kindness and compassion. I worry that all the trauma she's already been through at such a young age will harden her heart.
See also: harden, heart

harden one's heart

Feel no sympathy for, as in We can't afford to give them more; we'll just have to harden our hearts when they ask . [Late 1300s]
See also: harden, heart