You don't have to tell everything you know. There are times when forgetting something you heard can be just as important as remembering—and more difficult. If you speak when you should not have, your regret may last a lifetime. There is nothing wrong with having nothing to say—unless you insist on saying it.
God's Word says if we don't control our tongue, we are fooling ourselves and our religion is worthless (James 1:26). There is a lot of bad in the best of us, and much good in the worst of us, so it doesn't behoove any of us to talk about the other.