Discoveries in physics and psychology undermined earlier ideas about reality and knowledge because they provided empirical evidence for the fact that not everything was as it seemed to be. The general intuitions about the world seemed to be false. One example was the discovery of observables in physics which seemd to change when being observed.
Another shocking discovery in psychology was the fact that people are narrativistic creatures as we're trying to creatue stories about ourselves and don't actually consider te actual data about what has happened in the past.