What makes a person truly happy?

Recently, a friend and I decided to spend the day out of town. We had planned a quiet picnic, but a heavy rain suddenly started. We took shelter in a small family-run café, where we met an elderly couple. They had been together for over forty years, yet they kept teasing each other as if they had just met. Before leaving, the woman said to me, "The most important thing is to choose each other anew every day." For some reason, those words really stuck with me. That is likely how happy relationships are built.