The word 精力 is formed by combining two conceptual characters: 精, which conveys the idea of the essence, refinement, or the most concentrated part of something (like the essence of rice or vital essence in traditional thought), with 力, which means strength, power, or energy. Together, they create a compound idea where 精 modifies 力, suggesting not just raw force, but the refined, vital, or quintessential energy that fuels one's capacity for activity and mental focus, essentially, one's concentrated vitality or resourceful stamina.