Justified, true beliefs: https://plato.stanford.edu/entries/knowledge-analysis/#KnowJ...

People who believe in "chemtrails" are (in my un-scientific survey) pretty likely to be conspiracy enthusiasts ("cranks", "crazy", etc.).

But they're not wrong that the stuff coming out of the back of jet aircraft is changing the climate.

Small, localized weather engineering programs have long been real (cloud seeding), and planetary-scale climate engineering projects are now openly discussed by governments. E.g. https://www.epa.gov/geoengineering/about-geoengineering "Types of solar geoengineering techniques include: Stratospheric Aerosol Injection (SAI) – adding small reflective particles to the upper atmosphere (stratosphere) to reflect incoming sunlight. Sulfur dioxide (SO2), one of the types of chemicals considered for SAI, can chemically react in the stratosphere to form reflective sulfate aerosols."

Galileo's heliocentric model

Hand washing prevents illness

COVID came from a lab, not a wet market

Hunter Biden laptop was real

And then a counter example of something broadly accepted but untrue. The humoral theory and blood letting, practiced for thousands of years. This is what killed George Washington.