Certain classes of UAPs demonstrate flight characteristics that are not possible given our current understanding of gravity and aerodynamics.
Dozens of credible eye witnesses from multiple countries; fighter pilots, commercial pilots, nuclear physicists, and high ranking government officials.
Source "In Plain Sight", US Navy fighter pilots David Fravor and Ryan Graves, etc.
People are quick to dismiss these stories as hoaxes or bad memory, but scientific discovery almost always starts with an unusual or unexplained observation.
Uranium was discovered in 1785 and ionizing radiation wasn't discovered for another 110 years in 1895. True scientific understanding of new observations takes quite a while.