I understand your concern and I'm not being sarcastic or negative in any way. This is a question many people ask and the easiest way I can think of to explain is this: It's all about "faith." For ex. When you sit in your chair, you sometimes don't even think of, "I wonder if this chair will break when I sit on it." We sit on the chair blindly knowing the chair will hold us. We sit purely on blind faith. People have been starving and dying ever since time began; the rich get richer and the poor get poorer. People make choices and sometimes we don't always make the right choices which cause "challenges" in our lifetimes. Personally, I believe if there is a Heaven there has to be a hell.