A knee jerk reaction is a quick response made without thinking carefully. This idiom is used to describe when someone reacts straight away without thinking.
The expression comes from a simple medical reflex. When a doctor taps the knee just below the kneecap, the leg automatically kicks forward without you meaning to.
The expression comes from a simple medical reflex. When a doctor taps the knee just below the kneecap, the leg automatically kicks forward without you meaning to.
His first response was a knee jerk reaction, but later he realized he needed to think about the problem more carefully.