Passion

I have written before of the importance of Product knowledge and Personality as critical ingredients for a good salesperson.  The third P is Passion.  Three legs of the stool: Product knowledge, Personality and Passion.  But not just the generalized notion of passion--but the ability to be passionate about what you're selling.  Product knowledge can be taught; even personality can be worked on; passion cannot be taught.
You know what you're passionate about.  I have a friend who gets very passionate about the subject of fusion; another who is passionate about rock bands.  But can you be passionate about refrigerators and air compressors?  Can you be passionate about Subaru's or a house you have to sell as a realtor?
Passion for selling as a career--not a job to create income for your true passion (whatever that is) is the first step on this path.  Passion for your product--truly believing that it is better than the other guy's, that it serves an important function for your customer,  that you truly believe in it, is critical to success as a salesperson.
Passion for your product arises out of product knowledge and knowledge of your competitors' product.  Passion for your product arises out of knowledge of your customer's business and how your product can improve your customer's business, or lifestyle in the case of a consumer product.
You can "feel" passion--when a salesperson believes in what he's selling.  That passion arises out of confidence in his product knowledge and confidence that he understands you as a customer.
Passion is the leg that the stool must have to support your weight.