Why do bad thing happen to good people?

First of all, humans are not good because the Bible says "No one is good, except God alone." Second, we live in a post-fall world with Satan and demons, and that sin has infected all of humanity. He allows the spiritual enemy to influence both believers and unbelievers. We cannot blame God for everything that happens in our life because everyone has the freedom to choose between right and wrong. Every unbeliever can choose to trust the God of the Bible and pray for His guidance in order to experience salvation in Jesus Christ. Unfortunately, innocent people are frequently caught in the crossfire as a result of the wicked actions of others. This is tough for many individuals since they do not comprehend how God works. If something happens in our life as a Christian, we simply need to be prepared to respond in the right way since this is His way of building our faith in Him and fullfilling His divine purpose. And I pray that when unbelievers face such horrible circumstances in their lives, they will begin to call on Jesus. 

As it is written: “There is no one righteous, not even one." - Romans 10:13

No one is good except God alone. - Mark 10:18

For “everyone who calls on the name of the Lord will be saved.” - Romans 10:13

As for you, you meant evil against me, but God meant it for good, to bring it about that many people should be kept alive, as they are today. - Genesis 50:20