public function fail($asString = false)
    {
        if (!$this->_checked) {
            $this->check();
        }

        if (!$asString) {
            return $this->_fail;
        }

        $items = [];
        foreach ($this->_fail as $rule) {
            $items[] = "{$rule}";
        }

        return implode(', ', $items);
    }