One of the most impactful Ted Talks I have ever seen was a presentation called "The Happiness Advantage: Linking Positive Brains to Performance" by Shawn Achor.
The presentation is about 6 years old but it is just as relevant today as when it was originally recorded. Check out the link above to judge for yourself.
One of the reason I love the talk is because of a key point Shawn makes which is especially true for folks in the selling profession. We are often conditioned to associate the achievement of sales goals and targets with the attainment of happiness.