To commit herself to becoming "an apostle of Joy" when humanly speaking she might have felt at the brink of despair, was heroic indeed. She could do so because her joy was rooted in the certitude of the ultimate goodness of God's loving plan for her. And though her faith in this truth did not touch her soul with consolation, she ventured to meet the challenges of life with a smile. Her one lever was her blind trust in God.
The tendency in our spiritual life but also our more general attitude toward love is that our feelings are all that is going on. And so to us the totality of love is what we feel. But to really love someone requires commitment, fidelity and vulnerability. Mother Teresa wasn't "feeling" Christ's love, and she could have shut down. But she was up at 4:30 every morning for Jesus, and still writing to him, "Your happiness is all I want."