It may not appear like that to us, but whatever wickedness he can design, it is always less than he might desire. He spends his time wandering to and fro. Philosophically, this tells that ultimate reality is not dualistic. Satan's power is not on a par with God's. There is no equality between good and evil.
Trials come as a result of Satan's malice.
Job was unaware of that, of course. He never gives Satan a mention. That is one of Satan's tricks. Then he can get on with his work without hindrance. We can, to cite Lewis, make too little of Satan.