But as the session starts - your hot idea may be a not idea.
You say it - and no one is impressed.
But something great happens in the process - ideas grow into an intertwined web - shared by everyone. Ideas spawn partly from inspiration. That inspiration often can come from confusion between people.
For example - a person will say their idea and someone else will interpret it differently. And thus a new idea is born. From both people comes something better.
And this is a great way for everyone to contribute to the end idea.
So even if you don't have ANY ideas, please say them - someone might confuse it for a good one!
PS. I've learned in brainstorming - it's impossible to come away and say, that was my idea - it's always ours.