How can Paul have joy while in Jail?

As we continue looking at the first chapter of Philippians, Paul will give his friends an update on how he is doing. But remarkably, instead of giving details on things that are frustrating... he speaks with joy. Abounding with joy. How can that be? Being in prison without having committed a crime would normally leave a person incensed at the injustice. Let's see what is driving Paul’s experience.