Great answer by Oliver. What I love most is being out and meeting people. Every new encounter is exciting.
What salespeople find most frustrating is what I call, "chasing rainbows". It's the idea that if I sell $100k this year, I will be expected to sell $450k next year. Sales goals always increase, but not necessarily the support.
Building loyalty with clients and creating a situation where you become their trusted advisor takes time, but I believe is the ultimate for a sales professional. Not only does it make you feel like you've accomplished something, it moves you up in the tax bracket.