I think they are just incredible because I'm the boss get me holla me
The sales department is the bread earner of the company as it generates sales for the company. The finance department makes the budgets and the target of the money it wants to earn to the sales department who translate it into the sales necessary to generate the finances. Sales department analyses trends in the market and keeping this in mind gives product specifications to the manufacturing department. Now, the manufacturing department can only produce if it has finances so the sales department interacts with the finance department to get the necessary funds. This is basically how the departments interact and often conflict erupts as the finance wants to cut cost while the sales people demand money for their projects.