The absence of 'feel' in the steering. The geometry of a vehicle's steering, particularly the castor angle, is designed in such a way that the driver can feel through the steering wheel the car's grip on the road and the turning forces. So if, for example, he drives suddenly on to ice he should recognize the reduced grip by the lower resistance to turning in the steering wheel. Alteration of the steering geometry may deaden this 'feedback', as happened with early power-assisted steering systems. Dead steering was the result.
Also see: How it Works - Steering