You hit the nail on the head. That's the problem - politicians aren't trained for the role they are expected to perform. In most countries, politicians are fairly educated characters who can perform a number of feats but usually lack understanding of the world around them.
The Greeks who invented democracy and various other forms of government recommended years of training for politicians and that included oratory, military studies, some philosophy, statecraft and various other skills.
Sometimes the rule got broken with unpleasant consequences. I guess the Romans did well under rulers like Trajan, Hadrian and Claudius but they had real problems with rulers like Caligula (who upset Israel with his plan to put his own statue in Jerusalem).
My favourite was Commodus (featured in the Gladiator movie). He believed he was a god, fought as a gladiator in the arena, kept hundreds of concubines and invested in as many gladiator shows as possible to keep the masses happy.
George Bush doesn't believe he's a god, of course, but just claims he has a direct phone- line for the odd chat with the Almighty (when he wants to discuss foreign policy).