The phrase "can't hack it" means to be incapable of handling a situation or task. The antonyms for this phrase would be "capable," "competent," "adept," and "proficient." These words imply that the person is suitable, qualified, and skilled at completing the task at hand. Other antonyms could include "succeeding," "achieving," "exceling," and "thriving." These words signify success and accomplishment, which is the opposite of not being able to handle something. When one is capable and proficient, they can take on challenges with ease and are more likely to thrive in any situation.