Heres a situation:
Man wants to commit suicide, he goes to shoot himself, the bullet bounces off a wall and hits two chemical beakers (he's obviously a scientist duh lol) these two chemicals make the cure for idk...aids,cancer,downsyndrome, and ugly.
However this man still wants to kill himself because he believes life is worthless, yet he had accomplished much.
Or a man has the motivation and believes his life is worth much, yet life has decided to give him every single bad pitch and he still lives out on the streets.
The only problem with your analogy is it doesn't account for the entropy of the universe.
Sorry, what I meant my comment to say was that the purpose of life means more to the person in question. I think I started off with that idea in mind but then kinda branched out.
What it was meant to say was, life will mean the same to this scientist guy whether or not he discovers the cure for cancer, as you've said. Thus, the significance of life can't be measured by one's impact on others, because some people simply don't care about others. However, with the people in your analogy, one thing is consistent. Their outlook on life remains the same no matter what; and that is my point. Their outlook on life determines their, well, outlook on life (obvious, right?).
So, for the first guy, if he thinks life is so insignificant that he doesn't want to live anymore, then finding the cure for cancer wouldn't mean much to him. Just in the same way as the second guy, who works his whole life and has bad luck, will never lose his outlook on life.
Now, I know that doesn't make sense. Because I know if I dropped a billion dollars accidently down the drain, I would be pretty miserable. And I know if a depressed hobo found that billion dollars, he'd be pretty overjoyed.
But I'm not talking about somebody's mood, or their current emotional state. I'm talking about their overall outlook on life. I'm talking about a person (person #1) who no matter the circumstances, billionaire or hobo, would think that life simply has no purpose, and person #2, who, in the same circumstance, would think he should still strive to fulfill his calling and make something of himself.
Person #1 and Person #2 will both always see life that way. If they choose to believe that their lives have or don't have a purpose, this will determine their outlook on life.
I know this whole thing has been rather rambling and circular, but, the point I'm really trying to make is (TL;DR) that:
We decide how significant life is to us.
So, really, you and the OP are kind of digging yourselves into a hole. In truth, it really is up to either of us to say whether life has a purpose or not. But by deciding that it doesn't, you're preventing yourself from ever creating a purpose for yourself.