Reserve Judgment

From Mugshot Developer Wiki

The suggested design process doesn't get to Choose until the fifth phase!

As an exercise, before you start with Define, you can ask everyone in the room to state their relevant agendas and preconceived ideas. For example, "I'm 100% convinced the only way to do this is XYZ" - let people present that point of view, then ask them to set it aside and focus on generating ideas for a while. Agendas can be picked up again to Choose, but surprisingly often there will be new paths available to choose from that nobody had in mind at the start of the process.

It destroys definition, research, ideation, and prototyping if someone in the room is shooting down everything and insisting they already know the answer; you will have to either make them stop or throw them out ;-)

Don't accept artificial limitations up front, either. Ask people to restate them as part of the definition - "what are we really trying to solve?" - but don't allow anything in the definition unless it's an intrinsic and essential element of success.