What One Quality Makes A Great Salesperson?

When running sales training seminars I often ask what attributes make a great salesperson. I get a multitude of answers but people often say things like…

… motivated, charismatic, tenacious, honest, goal seeking, driven, positive mental attitude, self-belief, knowledge…

Today, I don´t want a list however… I´m just real curious… If you could only choose one quality and one alone, what ONE quality do you think makes a great salesperson?