Don’t try to define everything. Not only is it a fruitless task that will forever remain beyond your grasp, it is counter-productive. If you wanted robots, you would have bought robots, not decided to work with living breathing socializing human beings. Robots are cheaper, frankly. No, you have humans around you that can think and decide and create and build. Some humans like things defined and concrete, and others like them abstract and loose, but nobody wants to live in a box.
One way to help those around you is do loosely define the broad roles of various people. Not “Sally staples the check stubs to the invoices once they are paid” but rather “Sally is responsible for paying vendors.” If Timmy is quite good at striking deals, don’t tell him he has a quota of 36.2 sales per month, but rather educate him on what constitutes a good sale, put “Sales Representative” on his business card, and call it good.
It’s important to give the people around you a mental model where they can place the others they’re expected to work with. But don’t attempt to make it a jigsaw, with hard boundaries that never overlap and must be fit together exactly. People will play by any rules given to them. Just make sure the rules are loose enough that the creative juices aren’t bottled up.