The cost of an unexamined assumption

When a plan fails, the review afterwards usually finds that the business knew more than it acted on. The warning signs were there. Someone had raised a concern. A figure looked odd. The trouble was rarely a lack of information. It was a belief that nobody examined, because everyone already held it.

The assumptions that get argued about are, in a sense, safe. If two directors disagree about whether a new market is ready, the question gets attention. People gather evidence. Each side tests the other's view. By the time the decision is made, that assumption has been looked at from several angles.

The dangerous assumptions are the quiet ones. They are so widely shared that nobody thinks to say them out loud.

What a quiet assumption sounds like

A quiet assumption sounds like common sense. Four examples show the pattern.

The dangerous assumptions are the quiet ones.

"Our customers will stay with us through the change." It feels true because they always have. But they have never been asked to put up with this change, and nobody has asked them what they think of it.

"The system can take the extra volume." It has coped so far. Whether it copes with twice the load is a different question, and the people who know the answer may not be in the room.

"The team will support the new structure." The senior people have agreed to it. Whether the people who do the daily work understand it, or see why it matters, is another matter.

"We can do this alongside everything else." This is the easiest to miss. Plans are drawn as though the business has spare capacity. It rarely does.

None of these is foolish. Each may well be true. The problem is that nobody knows, because nobody has checked.

Why they go unchecked

Shared assumptions go unchecked for good reasons, which is what makes them hard to catch.

They come from experience. The people making the decision have watched the business work a certain way for years, and their experience is usually a sound guide. It is a poor one when circumstances have changed in ways that are not yet visible.

They come from agreement. When everyone around the table holds the same belief, nobody feels the need to test it. Agreement feels like confirmation. It only shows that everyone started from the same place.

They come from pace. A decision that has to be made quickly leaves no time to question what feels obvious. The questions that get asked are the ones in dispute.

How to find them

Finding a quiet assumption takes deliberate effort, because by definition nobody is pointing at it.

One method is to write the plan out in full and underline every statement that no evidence supports. This is slower than it sounds and more revealing. Many plans turn out to rest on more belief than anyone realised.

A second is to ask what would have to be true for the plan to fail. People find it easier to imagine failure than to list assumptions. Each way the plan could fail points to something the plan takes for granted.

A third is to ask someone outside the decision. A person who does not share the experience behind it will question things the people inside it no longer see. This is one of the plainest reasons to bring in an outside adviser. The adviser does not know the business better. The adviser has not yet learned what everyone inside it assumes.

What to do with them

Once an assumption is in the open, a business can do one of three things with it.

It can test the assumption now, if testing is quick and the stakes are high. A few conversations with customers, or an afternoon with the figures, settles many questions in days.

It can build the plan so that it does not depend on the assumption. If the business is not sure the system will cope, it can phase the change and check at each stage.

Or it can accept the assumption knowingly, name someone to watch it, and agree in advance what would show it to be wrong. An assumption accepted with open eyes is a risk being managed. An assumption nobody has seen is a risk being ignored.

The habit to build

The cost of an unexamined assumption is not paid when the decision is made. It is paid later, when the plan meets the business as it is, and the business discovers what it believed without knowing it.

The habit is simple to state and hard to keep. Before a significant decision, ask what everyone already agrees on, and check that first.