There's a simple reason why so many brainstorm sessions are a waste of time. The problem statement being pitched to participants is the wrong one.
This is not surprising -- especially when you consider how little time most facilitators put into preparing for a session.
Here's what happens: The person who calls the session is usually scrambling -- overwhelmed, over-caffeinated, and running from one meeting to the next. Out of breath, they pitch the topic to the group, but the topic is either vague or secondary to a more essential challenge that remains unspoken.
G.K. Chesterton, one of the most influential English writers of the 20th century, distilled the phenomenon down to 13 words. "It's not that they can't see the solution," he said. "They can't see the problem."
Then, of course, there's also the phenomenon of perception bias.
Pitch a challenge to an IT person, and it will be seen as a technology problem. Pitch it to a CFO, and it will be seen as a financial problem. Pitch it to a marketing person and it will be seen as a branding problem.
Or as a wise man once said, "When a pickpocket meets a saint all he sees are pockets."
If you plan on running an ideation session any time soon, don't just stumble into the room and pitch a vague topic to the group. Do your homework. Make the effort to identify the REAL issue before asking for ideas. If it's the WRONG QUESTION you present, no amount of idea generation is going to make a difference.