It is said that one needs to remember the past, so as not to repeat it. Of course, that only applies to the errors.
In July 2016, members of the Black Lives Matter movement engaged in a peaceful protest in Dallas, TX. They accused law enforcement officers of targeting blacks, in unlawfully killing African-Americans merely for the color of their skin. Protesters, and officers, posed for pictures.
Some hours later, fourteen Dallas officers were shot. Five died of their wounds. While the sniper was still selecting target officers, officers shielded, protected and evacuated some of the same marchers.
This is a bit of history we might want to remember.