SonA (my five-year-old) is a really good helper... most of the time. But sometimes he'll start a "job" and about halfway through tell me, "I can't do it anymore." I tell him of course he can and he'll respond, "But it's hard!"
Isn't that the truth? With my son, I cheer him on, tell him he can do it, and that most things that are worthwhile are hard. He has to yet to be unable to finish the chore or project he was working on. That is a life lesson that is worth learning young. For most people, most of the time, anything worth having or doing takes work. And usually, it takes hard work.
My mom had a saying growing up that she repeated to us over and over. "A job worth doing, is worth doing well." I hated that phrase when it applied to cleaning my room, or the bathrooms, or whatever chore she was referring to. I was more of the "a job I have to do is only worth doing as well as necessary to make Mom let me go do what I want" mentality. But guess what? She was right after all dangit, and it's a good thing she didn't give up telling us that, because it is true for a whole lot more than housework.
Writing is hard. Trying to get an agent is hard. Trying to get published is hard. But you have to do your part of the job, do it well, and then stick it out.
"But it's hard," you say? Yeah, I know. Trust me, I really, really know. But if it's something you really want, it's worth it, right? So we all keep working at it, and working at it, and we will all make it where we want to go if we don't give up.