By learning to reply, "I don't know," you will save yourself from embarrassment.
When you try to answer something you are not certain about, you are setting a trap for yourself. You hesitate to say, "I don't know," because you fear disapproval. But if others find out you gave them misinformation, you will suffer even more disapproval.
Consciously make an effort to say, "I don't know," whenever you are unsure. Write a list of times when you answered, even though you did not know if what you were saying was true.
When you say something wrong, admit to people that you made a mistake. If you have the courage to do this, you will no longer fear saying, "I don't know."
(Talmud Brachot 4a; Rabbi Pliskin's Gateway to Happiness, pp.262-3)