This goes to the heart of the amount a territory can produce, or, a sales person can produce.

Quota’s need to be designed so that the sales person is motivated enough to achieve them make their money's, and stay at the company and not be so that the company loses money, or they are never achievable

The reps often leave because the quota is not achievable and consequently the rep does not make money and leaves – resulting in the territory being vacant and the cost of finding, hiring and ramping a new hire