Target fixation is a process by which the brain is focused so intently on an observed object that awareness of other obstacles or hazards can diminish. Also, in an avoidance scenario, the observer can become so fixated on the target that they will forget to take the necessary action to avoid it, thus colliding with the object.
This is a common issue for motorcyclists and mountain bikers. A motorcycle or bicycle will tend to go where the rider is looking; if the rider is overly focused on an obstacle, the cycle can collide with that object simply because of the rider's focus on it, even though the rider is ostensibly trying to avoid it.
The term target fixation was used in World War II fighter-bomber pilot training to describe pilots flying into targets during a strafing or bombing run.