"I find it can be a challenge to move from the brainstorming phase to a solid concept with a defined action plan and timeline. Some of the individuals I work with in creative roles do not enjoy reigning in their ideas because they feel it limits them creatively.
I have found success in asking them to agree to a solid outline, and then filling in the details creatively as they go as long as they can keep it within an agreed upon timeline or budget. I check in with them regularly during the development process and offer support and assistance as roadblocks or scope issues occur. That approach typically offers them some freedom while maintaining the structure necessary to complete projects."