Someone vomited in the hallway.

Several people walked right past it and did nothing. Most of those that did notice it acted as if they hadn’t.

At least one of the people who didn’t notice it stepped in it.

Three people, walking through the hallway together, saw it and gathered around it. They discussed various aspects of the vomit: the possible origins of it, why it had occurred, what to do about it.

These three people decided that they would do nothing about it. They also decided they would tell nobody that they had seen it and decided not to act. They formed an informal pact to hide their secret.

One person saw it, and as a result, vomited a few minutes later. They did not tell anyone.

Someone noticed it and expressed their disgust at both the act and the product of that act. Finally, this person decided to call maintenance and have it cleaned up.

When he got home that evening, the janitor that cleaned it up did not tell anyone that he had cleaned up vomit at work today.