humans have a great way of thinking of causes and effects.

something must have caused us to be here. but i don't think that the question is asking what causes us to live. it's more about our purpose and justification.

if the question is about serving some greater purpose.. who knows? we certainly serve purposes for each other all the time. a farmer may serve the purpose of harvesting food. a mother may serve a purpose of feeding a child. a teacher may serve a purpose of helping to raise a child, etc, etc, etc.

i suppose we even serve purposes for plants and animals, including the microorganisms that live in our bodies.. viruses, etc. in fact, we serve the purpose of continuing certain species. i wonder if the corn and grass and flowers etc. are thankful that we have a hand in continuing their legacies.

if you're looking for some objective justification, something outside of humans, then the question is flawed and unfair. we can't really decide as if we are not humans. we can't escape that. we have to answer the question as humans. who else do we have to justify it to? aliens?

the fact is, we decide the reason. it's a totally subjective question.

it's up to you to decide for yourself! who's to say that you, personally, have no reason to live? i wouldn't listen to that person if i were you.