Just like the father who son was possessed by demons, ask for help. This father took his son to Jesus and asked Him to remove the demons--if you can. Jesus told the father, "All things are possible to those who believe." If Jesus said it then, He says it now. You just got to believe. If you are still struggling with the concept, then just like that father, ask Him to help you overcome your unbelief.
As a believer, we have a Savior that always has our best interest at heart. You may not understand the test or the trial. Still there is Someone watching out for you and the changes you deal with. Therefore, trust God. Believe in Him. These vicissitudes are nothing compared to the God we serve. So if something comes along that causes you to not believe, ask God for help. He will oblige.
Soli Deo Gloria,