My definition of stress is that it is the psychophysical response that is triggered by the perception that you are out of control. For example, when you are faced with a problem that you cannot solve by the body of knowledge that you currently have, you are under stress. When you are faced with a challenge or problem that is bigger than anything that you have encountered before, you are naturally under stress. In this sense, it is the most salient element that triggers and compels transformation. That's why I often tell my students to ask themselves a question for which they have no answer, or read a book that they cannot readily understand. That causes stress. And by the time they become able to answer the question or understand the book, they have evolved. -
YASUHIKO KIMURA