give an example of contributory negligence?

A person digs a hole in their yard a big hole. They do put up a sign but not any barrier around their hole. 

A man walking on the sidewalk sees the sign but goes into the yard anyway and falls into the hole and is killed.  His family sues.

The homeowner says there was a sign. 

The family says it was dark and there was no physical barrier. Each is negligent.  But the dead Man should not have been there and contributed to his own injury by trespassing.

"The failure of an injured plaintiff to act prudently, considered to be a contributory factor in the injury suffered, and sometimes reducing the amount recovered from the defendant."

An example is when you're the "president" of the United States and you ignore the guidance of scientists and doctors in the midst of a pandemic to further your political aspirations.