Jeff Gothelf has a great post that brings together Product Managemet and my preferred philosophy, Stoicism.
Understanding our customers’ users is key to building products they’ll both love. Measuring your success based on your customers’ behavior is the only way for you to know for sure whether or not you’re delivering value and solving a real problem for them. Any user behaviors that are one step removed from your direct influence pose a risk to your key results.
He doesn’t say stoic anywhere in the post but the core value is there. Stoics teach that you can find happiness by learning to not worry about things outside of your immediate control. In this case your customers customers are out of your control, and you shouldn’t set goals based on their behavior.
Left unsaid, you also should be careful setting goals based on what sales and support are doing. You can’t control if your sales people pitch well or get the pipeline they need from marketing.