Why are we born different?

Why are our lives so different?

Some are kind, some are cruel. Some are beautiful, some not so.
Some are smart, some dumb. Some people get lucky. Some are healthy. While some suffer from chronic illness. Some live long, some die young. Some are happy, some are in pain.....the list goes on.

Why is we so difference? Is life just natures gamble? Or is there a reason why we are how we are?