Sacrifice does not mean loss, it comes from sacra facere in Latin. It means to make holy.
Sacrifice is not feeling bad so others can feel good, not by its definition. It is an example, yes, but not its totality. Altruism is holy, but not the definition of holiness.
The purpose of this life is to cooperate with the Grace of God like a plant does with sunlight. To make oneself holy is the goal of this life and the next.