Some people learned to be fearful.

At some point I was working on a piece of software we knew inside out, had good tests for and often ran through hand curated stress tests for benches, analysis or just exploratory testing, so we had a high confidence in it and in our ability to modify it quickly and successfully.

Some day executives were visiting and we had to do a demo of our system interacting with another one. Until the last minutes we were happily modifying our code to make the demo better. A guy from other system's team saw that, freaked out, and went straight to our boss, who then laughed with us at how scared the guy was. It turned out his team was not at all that confident in their system.