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

B: Don’t be discouraged. Just ignore him. It is a knee jerk reaction for George to criticize anyone who makes efforts to change things the way they are, for better for 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. The term began to be used figuratively from the early 20th century onwards. For the above example, we can also say that “George is a knee-jerk critic of something new.”