In just about any job, you generally have a set of general company goals and employee specific goals that you are evaluated against. These evaluations will determine many things such as raises or even if you KEEP your job (for those that do their jobs poorly).
Salespeople likely have these same things but there is ONE overriding factor above all else: The dreaded QUOTA. What is a quota? The amount of revenue (aka "dollars") that is required to be brought in by a salesperson over a given time period (monthly, quarterly, etc).
If you've ever wondered why salespeople are so pushy when it comes to homes, cars or other things they sell, the quota is the reason why. If salespeople don't meet their quota consistently, they don't have a job. Sales is a tough job and I've asked various salespeople why they work in the industry. The respond that they like the challenge of selling and the excitement of closing a large deal.
The flip side of this is that even if the salesperson does everything 100% correctly, their jobs and livelihood could depend on the consumer signing the contract. Imagine if all your jobs were dependent on others?? The only other job I can think of that could even be close if Project Managers. Project Manager have to depend on other people to get their jobs without being their direct manager. That poses challenges in of itself.
Prior to my time as a Sales Engineer, I didn't really understand the sales process and what salespeople went through. As I've been supporting a sales team for the past few years, I've gotten a great understanding of what the salespeople go through on a daily basis and they have earned my respect.