The world is truly an unfair place; there's no way around it and it's is very normal to think about why people often go through difficulties regardless of what their backgrounds might be.
We need to remember what Jesus said in John 16:33 "In the world you will have tribulation. But take heart; I have overcome the world.” God had never said that we will not face tribulation and hardship, however He did mention that He will always be with us to make sure we are forever spiritually rich!
I cannot really answer why exactly suffering happens as each person has their own history but I can list down a few points that generally explain our condition and remind you that Jesus has actually given freedom from worrying.
1) We are currently not in God's original plan - We need to go to the very first book of the Bible for this one (Genesis - the beginning). God's original plan for us was to be with Him in the Garden of Eden - a place with no violence, killing or scare resources. Once man (i.e. Adam and Eve) had sinned against God by not trusting in Him and going their own way, God had removed them from the Garden and sent them to the earth where we currently live as a punishment. This is why you will hear many Christians say that this is a 'fallen world' - a world that does not provide the protection and safety that we receive in the Garden of Eden.
2) Spiritual forces - following the point above, since we are in a fallen world we do have to face the presence of evil forces or spirits who aim to destroy our relationship with God by putting obstacles like 'bad things' to try and weaken our faith in God.
3) Tests - If we look at things on a short term basis yes it does seem like bad things happen to good people; however if we look on a long term basis we often see these good people come out of such situations stronger and more faithful. God often puts us through tests which may seem heartless at first but are very much needed for us to realize how much we need God in our lives. He tests us but also keeps us safe during these tests and gives us a way out. Hardship often makes us grow stronger. If we use a story from the Bible as an example, we see the Israelites as slaves in Egypt for 430 years until they cried out to God (something they did not do the entire time while being slaves). They had accepted their slave status for all those years until they realized that, with God, they can grow to something much bigger - like how we see Israel being such a strong nation in today's world.
4) Free will - God has given man free will to make our decisions, right or wrong and with those decisions come consequences that affect other people as well. Linking this to Romans 3:10-18 we see that humans by nature resort to sin and have this internal greed no matter their background or how good they seem to be in society. So you might ask, why has God given us free will if we are sinful by nature? 1 John 4 says "God is love". Now since God is love, there has to be free will because if there is no free will, it forceful obedience rather than love. Love cannot exist without free will.