Sales is all about human interactions. A salesperson has to understand what's the right way to talk to others, how people perceive the product and how to
convince prospects to take the next step and close the deal. Understanding psychology can help you to understand your customers - their thoughts, needs and decisions. And most importantly: it can provide you with powerful tools which will help you to convince your prospect more of what you are saying than simple words in a sales pitch.
You might think that most of consumer's buying decisions are based on rationality and facts. But the majority of people base their decisions on many irrational factors - to later rationalise their decisions with logic. Understand those irrationalities in human behaviour to understand how to persuade better and sell your product.