protected function whyCantAlias()
    {
        if ($this->isSomeOriginalPageAnAlias()) {
            return t('It\'s not possible to create aliases of aliases.');
        }
        $destinationPageChecker = new Checker($this->getDestinationPage());
        foreach ($this->getOriginalPages() as $originalPage) {
            $originalPageChecker = new Checker($originalPage);
            if (!$originalPageChecker->canMoveOrCopyPage()) {
                return t('You don\'t have the permission to create an alias of the page "%s".', $originalPage->getCollectionName());
            }
            $originalPageType = $originalPage->getPageTypeObject();
            if (!$destinationPageChecker->canAddSubpage($originalPageType)) {
                return t('You do not have sufficient privileges to alias the page "%1$s" under "%2$s".', $originalPage->getCollectionName(), $this->getDestinationPage()->getCollectionName());
            }
        }

        return '';
    }