Amy Cuddy had a severe head injury which decreased her IQ making her not as smart as she had originally been.Most head injured people can not complete college after such an accident. So some of what she says you will not understand the significance of it unless you know the above.

What is the most important lesson to be taken from the video?

https://www.ted.com/talks/amy_cuddy_your_body_language_shapes_who_you_are