There is no excuse for poor preparation
The politician's trade is something best learnt in practice: that is the prevailing consensus in many political parties. Of course it is true that there is no school like the school of hard knocks, but that is no reason to throw aspiring politicians to the wolves without any preparation whatsoever.
Political skills can definitely be learned. The extent to which political parties invest in this, however, varies greatly. In my opinion, a party's professionalism is directly related to the amount of attention devoted to training these skills.
There is no excuse for poor preparation. The politician's trade, like any other trade, requires constant training.