Sometimes, the one who keeps us down is our very own self. That voice behind our heads telling us that we can't do amazing things. It's our very own demons and we know exactly who they are: those who we see in the mirror.
These demons have names. One that easily stands out is named Corruption, he just knows how to taint and rationalize everything. There is also one who is called Self-Doubt, and another who is called Laziness. Those two often work together to achieve a state of procrastination. Another one is called Frailty which just slouches down in a corner, constantly blaming everything. I am quite sure you are now seeing in your head that there are a lot more of them; each one peculiarly egging you notice them.
These demons exist primarily due to the absence of discipline. Lack thereof is what allows such demons to thrive. Now to be aware of them is one thing, while dealing with them is another.
To eliminate them, the first thing to do is to acknowledge their existence. And until we are ready to accept the fact that the demons inside of us and ourselves are one and the same, victory over them is a pipedream. Next, the resounding course of action to ward of these demons is to instill discipline upon yourself. This entails discipline in ever facet of your life. There should be discipline in food, work, entertainment, even rest. It may be a herculian task, but the path towards self-discipline begins with day one.
Self-discipline is essential for growth and development.