i believe it all comes down to sin.
dogs bark because they are dogs. mankind sins because we are sinners. unbelievers are in bondage to sin. those of us who believe in Christ Jesus still sin, but we have been set free from the bondage of sin. in other words, once a person becomes a child of God... (you have to actually
become Gods child by believing in Jesus Christ, none of us are born automatically children of God until we can understand the Gospel and put our faith in Jesus.)........
Once a person becomes a child of God they are indwelled w/ the Spirit of God which guides them in truth and gives them power over sin as long as they walk in the Spirit and obey the word of God. a lost person does not have Gods power over sin and a saved person who is living a life of disobedience to God is capable of sinning just as if they were lost. the difference is, God will chastise the saved person because they are His child.
there are many reasons why God allows bad things to happen. I dont understand all of them. i dont understand why God doesnt intervene all the time. There is coming a day when we will see God face to face and understand all. For now we dont fully understand Him. Gods word describes this here:
1Corinthians 13:12 For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.
so.. we only know in part now, we will fully understand when we see God face to face.
Also...
here's an article that will help you understand why bad things happen.
Why does God allow people to suffer?