Any jackass can kick down a barn, but it takes a good carpenter to build one.
—Lyndon B. Johnson

If there is a risk of enthusiastic clients over-estimating what is achievable, there is an even bigger risk that there will be a chorus of critics who say nothing is possible. Of course, you should address critics with a solid plan and concrete data. But they may attack your data and credibility, leading to a game of “he said—she said.”

In The Art of War, Sun Tzu dedicates a full chapter to “The Use of Spies.” He describes five kinds of spies:

1. Local. A person who has expertise in a certain area.
2. Inward. A person who works for the enemy, in this case the critics.
3. Converted. A spy originally in the employ of the enemy, but now in your employ.
4. Doomed. A person who is spying on you to whom you give erroneous information for that person to report to the enemy.
5. Surviving. A person who brings back information from the enemy.

It may be insightful to consider Sun Tzu’s definitions and ponder who in your customer’s organization may fit them.
 

Sun Tzu offers the following guidance for dealing with spies (I have substituted the word “critic” for “spy.”).

There is no one in the organization with whom the leader should have a more intimate relationship than the critics. Also, no one in the organization should be more liberally rewarded by the leader.

Critics must be managed in straightforward and benevolent ways. Playing games with them will not engender the service you want.

Be careful in trusting information reported by the critics.

Use critics for every kind of business. But be very, very subtle in using information provided by critics. In no other business should greater secrecy be preserved.

You need to understand critics’ views and how those views are circulated. Then, and only then, will you have all the information you need to formulate and communicate what changes are achievable. So, in keeping with your position of detachment and diplomacy, visit the critics often. Understand them. Convert them.

Identify people who are playing in the various spy roles. Embrace critics and understand them. Try to convert critics, or broker agreement with them.