Upon giving birth at an advanced age, Sarah remarks: “Laughter has God made me, Whoever hears will laugh at me.” Rashi explains that not only were people laughing at Sarah but they were also laughing with Sarah: for many prayers were answered on that day and there was great rejoicing in the world. Why only when Isaac was born did this happen? Abraham and Sarah connected with a broad array of people and many were genuinely happy for them. When you share in someone else’s joy, explains R. Shteinman, then this opens the door to God building on your joy and answering your prayers.