Suppose your little lad of five years of age is on his way to first grade, when suddenly Butch steps out from his place of hiding and beats your son up. So, the next day you walk to school together. Several days go by and you see no further sign of Butch. After a while your son says, "I guess Butch has moved away. Now I can go to school on my own."
So, off to school he goes, when suddenly and without warning he is pounced upon once again by Butch, who had never left, but instead had stayed in the shadows. He was there. Waiting every day, watching and observing us as we walked to school together.
So it is in our relationship with Christ - and our complete surrender to him, that we become totally dependent upon Him. It is that surrendering process which enables Christ to fully and completely take charge of our lives. It gives the Son of God our permission for him to watch over us and to fully protect us.
So satan cannot affect us as long as we walk with Christ and look to The Son Of God to fight our battles for us. And a very good Bible verse to help you remember this fact is John 4:4, "Greater is He that is in you, than he that is in the world."