The Devil, numbered XV (that's fifteen in Roman numerals), is about vice, the misuse of power and control, addictions and beliefs that steer you away from whole hearted healing and being. Virtues turned inside out into extremes, bastardizing intentions and meanings. False beliefs that vilify life in the flesh. Using the sensual to harm life instead of to edify life. The Just World Fallacy.
When in the obstacle position the Devil indicates staying in a bad situation, refusing to see that the qualities of honor, loyalty, safety, love, and other good qualities you have, are being exploited, or used against you. There's gaslighting going on. And self-deception to the point where you are not only hurting yourself but others as well.
When the Devil is in the solution position it may be one of those times where it's better to with the devil you know than the devil you don't. Also, sometimes, love can hurt, light can hurt, it's all too much, so the positive can feel like a devil hounding you. So, sometimes, that's the "devil" you need to listen to, or conversely, perhaps you are the "devil" by being a force of light and love in someone's life.
NOTE: Picture spot intentionally left blank. NO pictures are used so that the meanings can be more easily applied to anyone using the Smith-Waite system (aka: Rider Waite Smith, RWS).