Yes, you are correct, but a demon can only hack and possess the human mind, if the human is willing and is too weak to resist.
When we exhibit negative emotions such as anger, rage, sadness, and ect, we become prime targets for demonic influence. When we are experiencing extreme emotions like rage, is becomes easier for us to sin, and that's all the leeway the devil and other bad spirits need to work their possessive influence on us. In a fit of rage, and/or other extreme emotions, we don't think and reason correctly, which makes possession easier.
Sometimes, demons don't need our emotions as leverage for their possessions, they can simply cause mental distress as a way to get inside our head. I've experienced this before, but by the grace of God, I made it. It's ok to be angry, and show powerful emotions, we just need to be sure to not let it get out of hand and not sin in the process.