Probably the worst enemy you'll ever face is the one you see in the mirror everyday. What you see is what you get, right? Not exactly. Mirrors can deceive, but mirrors can also be broken.
As a first time entrepreneur, I've discovered that you need to have thick skin while holding a sledgehammer. People will say things that will dishearten you question your endeavors. So what? Step up. Even you will think of thoughts that will bring your own spirits down. So what? Tell yourself to shut up, and step up. When you look at the mirror and see a person that feels sorry for themselves realizing they can't make their business successful, take that sledgehammer and shatter it to pieces.
Perception is not reality.