Complex sentence: Narcissistic personality disorder is different than having a strong sense of self-confidence; people with NPD value themselves over others to the extent that they disregard the feelings and wishes of others and expect to be treated as superior regardless of their actual status or achievements.
Split into simpler sentences: Narcissistic personality disorder is different than having a strong sense of self-confidence. This is because people with NPD typically value themselves over others to the extent that they disregard the feelings and wishes of others and expect to be treated as superior regardless of their actual status or achievements.