If you want to be a bad product manager, develop your plans for new enhancements on your own. You’re the manager of the product so it’s your decision what comes next for the product. Why would you need to discuss that with anyone else? Don’t bother talking with your sales staff about whether you could get additional revenue with the new features. Don’t check with marketing to see if they have the resources to support the promotional plan you’ve devised. Don’t talk with engineering to get estimates on how much it will cost and how long it will take. Don’t get input from user experience designers on the impact these new aspects will have on the usability and utility of your product. At some point you can figure those things out, but you don’t need to work those things out until you start working on the new enhancements themselves.
If you want to be a good product manager, involve stakeholders as you plan additional projects and changes. While you as the product manager should be the authority and have the decision about what the product should do, by no means should that be developed in a vacuum. Keeping stakeholders in the dark is a bad idea for three main reasons:
As a product manager, you should work closely with others within your organization to plan upcoming projects and enhancements to get the appropriate accurate detail around your plans, obtain good ideas and suggestions from all areas, and increase the likelihood of buy-in and eventual project success. Keeping plans to yourself is a bad and short-sighted strategy that is bound to create problems and thus should be avoided except only in extreme circumstances.