That’s a major question in philosophy and religion which the Wall won’t pretend to have a simple answer to. For a philosophical take, you could look at the Stanford Encyclopedia of Philosophy’s article on pain: bit.ly/bc-pain. The Encyclopedia of Religion can talk you through Jewish, Christian, and Islamic responses to that question: bit.ly/bc-suffering, but also take a look at the Buddhist view: bit.ly/bc-four. TLDR: Everybody agrees it seems to come with being human. Some view it is punishment for sin, or a way of testing faith. Others see it as the nature of reality.