What's the hardest thing to do in Taekwon-Do? The answer depends on who you ask. For some, it's getting the hang of the sine-wave motion. For others, perhaps it is overcoming nervousness about breaking, sparring -- or doing them in competition. Third dan students would probably uniformly say, "Juche".
All of these can be difficult, for one reason or another, but they are all things that can be studied and improved in the dojang. Diligent practice will make your punches and kicks better; all you need to do is keep at it. Patterns that seem difficult at first do gradually improve as you become comfortable with the new motions, the new techniques. Once a tournament is over, you realize it wasn't as scary or intimidating as it first appeared.
Perhaps the most difficult thing in Taekwon-Do isn't any complicated pattern or super-athletic flying combo kick. The most difficult thing is simply walking in the door.
Once you're actually in class, with other students, peer pressure starts to take hold; humans are social creatures, after all. There will be an instructor, giving you encouragement, things to focus on, information to learn; all you have to do is pay attention. Even if you're just going through the motions, chances are you'll start to have fun, you'll start to get the rush of endorphins from exercise, you'll start to enjoy even the difficult aspects of the art. But that can only happen when you're in class; when you've decided to get off the couch and drag yourself to another workout, even if you don't feel like it. Wanting to improve is necessary, but not sufficient; you have to take that first step. But if you do, everything else will follow.
Like most lessons from the dojang, this idea carries outside of class, as well. Ending a bad habit, or looking for a new job, or moving to a new place, or asking out that guy or girl you're interested in . . . wishing, wanting, and hoping isn't enough. Deciding isn't even enough. You have to walk in the door.