A: I wonder why he picked on my proposal. I’ve done a lot of research writing it and I’m pretty confident that it will work.

B: Don’t be discouraged. Just ignore him. It is a knee-jerk reaction for Mike to criticize anyone who makes efforts to change the way things are, for better or for worse.

Note: A knee-jerk reaction is a “quick and automatic response.” This idom comes from the tendency of the knee to jerk involuntarily when hit sharply, properly called the patellar reflex. That was recorded by Sir Michael Foster in his textbook of physiology, 1877: Striking the tendon below the patella gives rise to a sudden extension of the leg, known as the knee jerk. The term began to be used figuratively from the early 20th century. For the above example, we can also say that “Mike is a knee-jerk critic of something new.”