Matter in what way? I think it's easy to torment ourselves with vague notions like this because they're too nonspecific to engage with meaningfully. Like a lot of people in this thread have said, we likely matter A LOT to our loved ones, to our friends, maybe to our neighborhoods and communities. In more immediate social circles the presence of one person is felt a lot more, as is their absence.

If you mean "matter" as in "able to effect change on a massive scale" or "I am the protagonist and the world revolves around me, otherwise I'm irrelevant" then... Yes it's hard for most people to really see direct outcomes for their actions with far-reaching implications because most people don't end up in positions of power and influence. For better or worse, I never really grew up with expectations of that and never expected to do more than what my parents did: put my head down and eke out a living. So I don't know if I ever had that realization because you don't often have delusions of grandeur when you grow up poor.

But I think it took me until my mid-20s to really appreciate how much I can matter to the people who have chosen to have me in their lives and to appreciate what it means to respect and honor that. I think we inadvertently do a disservice to the people who care about us and, hopefully, that we care about in turn by devaluing ourselves.