Apart from what everything already said about road surfaces, tyres and heaven knows what else, I honestly do believe that a lot of the problems experienced by so many cyclists are associated with their ability or inability to relax.
In all the sports I have competed in throughout my active life, I have always found by a very significant margin that if your are not relaxed then it is highly unlikely that you will be able to perform to your best ability.
Be that in golf where most peoples hands hold a club far too tightly which in turn tightens up the muscles throughout their body, or driving a car when in areas of extreme concentration in fast driving or hazardous conditions the vast majority of people simply hold the steering wheel far, far too tightly, or skiing when they don't keep their legs and torso loose and finally in cycling, as in the case in question when they tend to go "oh sh*t" and their body simply locks up solid.
There are tests and exercises anyone can do to increase their levels of balance and as you get more accustomed to these tests they all become easier and as a direct result the entire body becomes far more relaxed the result of which is that a more relaxed body is far more likely to react far, far faster. As a direct result of these exercises it is quite amazing how much better your overall levels of performance will very significantly improve.