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 George to criticize anyone who makes efforts to change things the way they are, for better or for worse.

Note: A knee jerk reaction is a “quick and automatic response.” This idiom comes from the tendency of the knee to jerk involuntarily when hit sharply, also called the patellar reflex. The term began to be used figuratively in the early 20th century. For the above example, we can also say that “George is a knee-jerk critic of something new.”