You shall not pass!
When Gandalf engages with Durin’s bane – a Balrog – he states, quite convincingly, “You shall not pass!” When the demon still advances, it meets the consequences and ultimately its death.
When Paul talks about the armour of God in Ephesians 6, he starts with stating the purpose of that armour: “so that you can take your stand against the devil’s schemes”. Unlike Gandalf, we are not alone in our struggles. The battle itself belongs to God; our job is to stand.
Is there anything in your life you are trying to accomplish in your own strength, which actually belongs to God?