Don't think so, maybe, pretty sure

Bruce Kodish and Suzan Presby have an interesting chapter in their book 'Drive yourself sane' with regard to truth and falsehood. They quote a story from the European undergound under Hitler, as written by Korzybski:

In a railroad compartment an American grandmother with her young and attractive granddaughter, a Rumanian officer and a Nazi officer were the only occupants. The train was passing trough a dark tunnel and all that was heard was a loud kiss and Vigorous slap.

Now ask yourself: what happened. On what assumptions are my conclusions based? How sure can I be of these assumptions? Note to yourself what your thoughts are.

After the train emerged from the tunnel, nobody spoke, but the grandmother was saying to herself, "What a fine girl I have raised. She will take care of herself. I am proud of her." The granddaughter was saying to herself, "Well, grandmother is old enough not to mind a little kiss. Besides, the fellows are nice. I'm surprised what a hard wallop grandmother has." The Nazi officer was meditating, "How clever the Rumanians are! They steal a kiss and have the other fellow slapped." The Rumanian officer was chuckling to himself, "How smart I am! I kissed my own hand and slapped the Nazi."

Now think again about your previous conclusions how sure were you and what right did you have to be so sure?

The GS idea here is that there is a complete scale from certainty to wild guess, not just a polar true and false. It is wiser to evaluate in multi-valued way instead of a two-valued way. Closest to certainty come observable facts like 'The tunnel was dark'. Closer to wild guess come statements of inference: 'Two persons kissed each other in the dark,' where you assume that a kiss is always between to persons. Most people would even assume that the kiss was between a male and a female person, which is an even wilder guess.

This insight has been very useful for me in project management. A thorough scrutinizing of my assumptions and inferences has led to many timely discoveries of project risks. So I try to avoid thoughts of absolute certainty in the new product development, since you need to make a lot of assumptions when discussing something that does not yet exist.
But avoiding certainty in project team meetings has caused great nervousness, stress and even hostility in some of my fellow team members! Why? In the team I have the role of an expert. People need to be able to trust me in my field of specialization. What specialist that avoids affirmations in his field of expertise can you really trust? How sure can you be the project will finish successfully without experts you can trust? Some people seem to have a hard time living with uncertainty. So my advice is: Watch out for them and be careful to reassure them without over promising!