Imagine: You are sent on a suicide mission for your government. You know you will not return. You volunteered. You believe that what you are doing will change the course of history. You are giving your life for the sake of your country, and you believe, for all humankind. You are optimistic.

Maybe it's not too hard to imagine with that illustration?

Now, imagine that you believe your duty is to save someone who is drowning, but you know you will die in the process. You engage in an act that kills you to save someone else...

There are various permutations.

Indeed, "believing others will be better off without you" is a self-defeating way of even seeing optimism in the world once you are gone. Almost like a scale of optimism and suicidality...