exactly my thoughts! someone to get even the opportunity to sit in such position should always had the training to do so. it is not like any random girl can take such position. and since he seems to fit the 'cultural expectations', he even allowing such change without reasons and not checking the girl capabilities is too dumb of his part, one mistake dumb enough to get his head rolling by his brother (giving the competition ammunition -_-).
he is only average tho, and not dumbed by love, what makes it even more tragic to him, as generally those novels talk about exceptions where guys are blinded by love or some kind of 'magic'. but he only made a dumb choice, he doesn't even seem too much of a idiot or incompetent... but he still made such a 'noob' mistake, that will cost him everything :O
Even if most those old timey political marriages were usually lacking in the love department, his attendant was right about how foolish he was to just hop on over to the sister without checking when he at least looked a little into his first prospective marriage candidate ╮(￣▽￣)╭
Poor prince has just enough brains to see his downfall through the whole ride lol.