When your organization wants to accomplish something, and the group that will address the project, change, or issue meets for the first time, that meeting is likely to be filled with what I call 'First Thoughts'. First thoughts are all about wants and needs, and you frequently hear those words pop up during this discussion. It's all about defining what you or your organization need or want.
Second Thoughts are exactly that - the other folks that are involved ask that all-important question (Why?), then proceed to tell you why the thing that you want or need can't be done, or how much it will cost, or how many man-hours it will steal from other tasks, etc. Second Thoughts are thinking about your thinking, looking for holes in the boat and kicking the tires good and hard before investing man-hours and money.
The author Terry Pratchett - our time's equivalent to Shakespeare - takes this process one step further, to what he calls 'Third Thoughts'. According to Pratchett, "Third Thoughts are thoughts that watch the world and think all by themselves. They're rare, and often troublesome. When a huge rock is about to land on your head, they're the thoughts that think: Is that an igneous rock, such as granite, or is it sandstone?"
Once you've heard all of the 'Why' answers, Third Thoughts are what lead you to re-examine the want or need in light of the organization as a whole, using the perspective of the other meeting attendees as the dental tool that looks for cavities. For this reason, it's always a good idea to involve people from other departments in at least the first meeting, even if their department is not involved in the issue. In fact, folks not involved in the issue are most likely to have Third Thoughts, because they have no vested interest in the outcome.
Pratchett also differentiates between 'Second Sight' (seeing what you expect to see) and what he calls 'First Sight' (seeing what's actually there). As you look at your list of meeting participants, think about who is most likely to have First Sight. If you don't come up with at least one name, you aren't inviting the right people.
Decisions cost time and money. Every mistake doubles both. The way to minimize risk is to put as much or more time into tire-kicking and perspective-sharing as you do into execution. Take time between each meeting to get it all down on paper, pass out the notes, and ask people to add what they've thought of since you met.
In the end, it will take less time and money to measure twice and cut once - especially if you figure out up front whether the cutting should be done with scissors or a chain saw.