The reality is, when your mood state is sour or low, you physically cannot deliver your best. You have voices in your head, limiting your concentration. Your appearance and tone betray your mood, taking away your ability to resonate.
Tim goes on to provide some advice on how to get out of the funky sour mood. It is good advice.
You need to be in a good mood for your interview, for your networking event, to help convey the good person that you are.