Everyone has his own secrets that he wants to keep even from his closest friends or partner or parents. Once the secrets are given away, his former personality and image will be affected more or less. As a result, he may lose his job, friends, partner and opportunities to rise if they are connected with crimes or immorality. So we can have own secrets as long as they are permitted by law and morality. I think it is impossible for two friends to have no secrets from each other. Sometimes preserving one's secret is necessary to acquire the friendship or love of another.