What: don’t talk about things that you don’t really understand (by the way, that’s the meaning of the idiom in the title… I learned it today).

Why: because you will get caught and you will look bad twice; first, because you were pretending to be smarter than your audience, second, because now someone in your audience will never trust you again.

How: ironically, this usually happens when we don’t feel confident enough about some topic. Therefore, the best way to fix this is

1. Doing good research before hand. Check all the concepts that you will discuss or expect to discuss during your presentation.

2. Being humble whenever you don’t know something. During a live presentation, this is my favorite answer to a killing question:

That’s a very interesting question that I can’t answer right now. Please let me check on this after the presentation and I will get back to you, thanks!

Toni Almagro (obviously is not mine, but I wanted to highlight it)

Where: this one is for presentations, but obviously is even worse in a written document… It will last “forever”.

And… here you have some final touch of humor!

I hope this helps!