While willpower can, on one hand, be used in dialog, it also enables you to withstand great pain. A character with high Willpower will not be distracted in combat even by heavy blows and will be able to complete their Special Attack or spell. Characters with high Willpower can also resist wounds better.
When your hero receives a wound, the game will automatically roll a Talent Test on Willpower with a penalty of 10. If the test is successful, the wound is prevented and the hero will not receive the corresponding penalties.