Ask “how do you know that?” politely and often. It sharpens everyone, including you.

Most claims travel without their evidence attached, and nobody checks because asking can feel like an accusation. Said kindly, the question is not a challenge but a request for the path, and it turns a conversation from a contest of confidence into something closer to working the problem together. People who genuinely know are usually pleased to show the route.

Try it once a day, with a friendly tone and real interest. Ask it of yourself as well, especially about things you have believed for years without rechecking. Notice which of your own opinions you cannot trace to a source.