How often do you challenge your assumptions and can you share an example?

Here’s my example: When I was a student I assumed that sending Germany’s oversupply of food into poor third world countries would be an excellent approach. Later I realized that this only makes sense in extreme situations such as natural disasters. Otherwise there’s great risk of destroying the local economies.

Here’s an interesting historical example:

“I have traveled the length and breadth of this country and talked with the best people, and I can assure you that data processing is a fad that won’t last out the year.” Editor, Prentice Hall Business Books, 1957

What about your assumptions? Do you challenge them from time to time? If yes, how often does this occur?