Threshold Concepts - Why learning new things can be (extremely) troublesome

In science education, students often face crucial turning points when confronted with difficult concepts or complex theories. For example, the so called threshold concepts are particularly interesting, as they alter the perception of scientific content and may even change the worldview. After this flash of insight, it is hard to revert back to the previous state. There is basically no way back to the original level of understanding. Once a threshold concept is understood, it may be hard to believe that you ever saw the world differently.