The opposite of weak-mindednesses could be strong-willedness, which implies a resolute sense of determination when it comes to making decisions. Someone who is strong-willed holds firm to their convictions and goals, and is not easily swayed by external influences. Other antonyms for weak-mindednesses include resilience, fortitude, and perseverance, which all describe a person's ability to withstand challenges and adversities. Additionally, intellectualism, shrewdness, and acuity could also serve as antonyms for weak-mindednesses, as they connote sharp mental faculties, astute discernment, and the ability to think critically and independently. Ultimately, the opposite of weak-mindednesses is a constellation of traits that signify a strong, unwavering character, and a mindset that cannot be easily shaken or compromised.