Assumptions are not evil. In fact, they are necessary innumerable times daily. We don’t have time to stress test every chair we sit in before we sit in it. We sit down and hope for the best.
The problem is not assumptions in and of themselves. The problem is the expectations we build on our assumptions. We expect that assumptions we made yesterday are still valid today, and so we expect the same performance today that was delivered yesterday. Further, and importantly, we emotionally attach ourselves to those expectations. “Hmm. I sat in this chair last meeting. The chair didn’t collapse. I didn’t fall onto the floor. No one laughed at me. I was not embarrassed.”
But what happens on the day the chair cannot perform as it did yesterday?
From on the floor, we call the chair, an inanimate object, names. We try to hurt its feelings the way our feelings have been hurt from being laughed at and therefore embarrassed. Further, we hold grudges against the people who giggled (because the incident actually was a little bit funny) even though they quickly assisted in helping us off the floor.
We behave irrationally because we were emotionally attached to an expectation based on an assumption.
Why? Because we did not expect CHANGE.