As soon as you begin a presentation and you turn out to be wrong (in the case of statistics), or unintelligible (in the case of the Jargon Trap), people begin to mentally step back from you. And if they do that, they have lost the message and you have lost the game.
Usability roughly can be defined as the ease with which a technology can be used, and the study of how different technology designs can either contribute to or prevent errors. In healthcare, this is a big deal because errors can have very serious negative consequences for the patient.
I often use the "I've slept since then" response, but it's still embarrassing and annoying to be that reliant on notes. I've often vented in frustration "Why can't I remove these 80's song lyrics from my childhood and use the space for the stuff I need to remember now?!"