Ever heard of the Semmelweis Bias? You've probably faced it.

In the mid 1800s, nearly 1 in 10 mothers at a leading European maternity hospital died from childbed fever after giving birth. A young Hungarian physician, Ignaz Semmelweis, made a simple observation. Doctors weren't washing their hands before delivering babies. In fact they were going straight from the morgue, performing autopsies to the maternity ward delivering babies.

When mandatory handwashing was introduced in 1847, maternal deaths fell from nearly 1 in 10 mothers to less than 2 in 100 within months.
The evidence was overwhelming. But the medical establishment rejected it for years. Not because the science was weak, but because accepting it meant questioning everything they believed to be true. Imagine that? A life saving idea, rejected because of ego and bias. In fact Semmelweis was committed to a psychiatric asylum near Vienna because they believed he was mentally ill.

Today, we call this Semmelweis bias.
And I see it in boardrooms all the time.
Leaders dismiss new ideas because they challenge old assumptions. They ignore changing customer behaviour because it conflicts with yesterday's assumptions.

The greatest risk is rarely a lack of information. It is our inability to let go of outdated beliefs. Consumers change. Market forces change. Culture changes.

The organizations that thrive are the ones willing to update their assumptions before the all the data and evidence becomes impossible to ignore.