The Devil as something hidden are those things you won't let go of, such as grudges, hurts, loss, etc. past relationships, things that belong in the past and do not serve you well. Negative thinking or self delusion fit well, because as long as you do those things, you can't progress and are stuck. People continue to do self destructive thinking or behaviors because they feel "safe" there, the devil you know... is less frightening than the devil you don't and have to find something else to replace it with.
Postponing happiness is one such thing, always making limitations just beyond one's reach, setting conditions that have to be met before a thing can be achieved, hold one forever away from the thing they believe they desire.
Things that hold you, like being a workaholic, obsessive behaviors, like spending too much time on the phone or internet, watching TV, playing games... things you know that aren't really helping you and hold you back. Using distractions to avoid dealing with things. Obsessing over anything, be it expectations, the proper way to do things become a form of self enslavement... even being or doing things you don't want to because you are afraid that it won't get approval or acceptance... allowing others to control you and not taking control of your life, actions, thoughts or feelings.
If you are hiding something from yourself, it could be owning up, taking responsibility for your feelings, thoughts, actions and behaviors... playing the blame game, if it weren't for this or that, then it would be different... so it's not my fault things didn't go the way they should.
Compulsive things too... like eating when you feel bad or to reward yourself or fill some sort of emptiness of the emotional sort... or retail therapy. Collecting things, even people to stroke your sense of self worth.
The biggest thing of the Devil, is doing the same things again and again and still bummed out when they still don't work, because it's easier to do the same old tried and failed stuff than taking a risk and doing something new and different because you don't know how they will turn out.
