Marketing works best when the effort you put into it is a little more than you think you need and a lot more than the market expects from your project.
And projects work best when the amount you need to get done is a little less than the resources you have available.
Marketing rewards a taut system, a show of confidence, the ability to be where you need to be with a true story that works.
Projects reward slack, the ability to keep your schedule and your quality, to watch the critical path and to make smart decisions.
The common errors, then: Pick too big an arena for your marketing, and seem underwhelming. And pick too big an agenda for your project, and run out of slack.
You have a bushel basket. The generosity of overflowing it makes it much more appealing when it's on the shelf. But when your job is to transport those apples, overfilling it even a little makes it likely you won't get to where you're going.
Make unexpectedly big promises. Keep them. Show up with enough resources to do both.