knee-jerk reaction

noun

Etymology: By means of an elliptical reference to the reflexes of reflex arcs, in this case the patellar reflex.

1. An instantaneous reaction made without thought.

   “Near-synonym: gut reaction”

   “But does the level crossing really need upgrading? Listening to Prosser, one gets the impression that this need to 'upgrade' is almost a kneejerk reaction. Although it is manually operated, Prosser thinks that the crossing is "pretty safe as it is", especially given the levels of traffic on the line. The signage, he says, could definitely be improved. But this relationship between who is responsible, either Network Rail or the local/road authorities, has long been a bone of contention. "In my experience, there's always a 'not my problem' attitude," he observes.”