I spend about half my time on marketing, and half on sales. The marketing aspect of my job involves a certain component of project management.
What I am finding these roles and tasks all have in common is the need for always thinking "what is the next step". If I talk to a prospective customer, I always need to ask myself and the client what is the next step. Should I schedule another call for next Tuesday? Find some additional information to email to the prospect? There should never be situation where I have not thought through and scheduled the next step.
If I am managing a project, and need someone else to do something for me. I need to stay on top of it, and make sure that the people I rely on schedule their next step(s).
In my experience, next step thinking is especially crucial for sales. A mediocre salesperson waits for things to happen; an excellent salesperson always thinks what is the next step.