Up until the mid to early 1900s, handwashing in medical care was nonexistent.
The man who issued the warning was ignored, shamed, and eventually went insane. Here is the summarized story:
Ignaz Semmelweis, a Hungarian doctor working in Vienna, noticed a disparity in deaths between two maternity wards in his hospital. So he collected data from each ward, one staffed by male doctors and medical students and the other by midwives. He found that the former had patients dying at a five times higher rate than the latter.
He found the male doctors and medical students would handle cadavers in the morgue before going to the maternity ward to deliver babies all without washing their hands, which was not a common practice at the time. (I kid you not... talk about 2020 privilege.)
So Semmelweis theorized that the handling the dead bodies might be playing a role in the higher rate of puerperal fever in the male-staffed maternity ward.
So he did a test and instituted a simple chlorine hand washing solution for doctors and medical students. Deaths fell immediately. He performed an experiment, collected data, and saved lives in REAL-TIME.
Did the doctors listen? Nope.
They did not like the inconvenient possibility that they might be responsible for patient deaths. So, as any good know-it-all human will do, they attacked the messenger. Ignaz Semmelweis was soon fired. He spent the rest of his life trying to convince (in vain) medical professions to wash their hands.
It wasn't until Louis Pasteur's germ theory became widely accepted that medical professionals started washing their hands... and only because of the social proof of the rest of the medical establishment. In America, it wasn't until the 1980s that the CDC started heavily promoting handwashing in response to an outbreak of foodborne outbreaks that handwashing became the standard we know today. That's 40 years ago, folks.
And here we are in 2020 thinking we know everything, just like the doctors in the early 1900s, the 1800s, the 1700s, etc.
I wonder what humans of 2100 will think about us. I imagine they will walk through their museums to view the primitive "tools" we use today next to a plaque explaining our rudimentary understanding.
Humans are dumb creatures designed by nature to do a few things very well in the wild. Yet today, we live in a complex world where everything in our environment is manipulated by man... to his own detriment.
We all must look to human history to understand where we came from. Human nature does not change, only the times. And those that forget history repeat it.
Finally, think 100 years into the future and imagine what humanity will see when looking back on 2020: a bunch of primitive humans with primitive ideas propped up by mountains of ego.