What is the difference between a narcissist and an optimist ?

I know that an optimist is someone who always sees the bright side of any situation and a Narcissist is a person who is overly self-involved, and often vain and selfish. But in a scenario where the outcome might turn out to be bad, an optimist is confident and hopeful that things will be better and even a narcissist claims that the outcome will be good if a good outcome is going to be in his favor, then how can one differentiate and tell whether its true optimism or a mask of ultra confidence.