Why do prayers from other faiths seem to work?

Salam alaikum. English isn't my first language, so forgive any mistakes. For a long time, I've wondered why our duas are accepted. But my real question is: why do the prayers of people from other faiths work? I’ve seen it happen. I live in a community with many different beliefs. My Jewish and Christian neighbors also pray, and I’ve noticed their prayers being answered. If their prayers are answered, doesn’t that mean there’s some truth or sacredness in their faith? (Hope 'sacredness' is the right word.)