It is hard, frustrating, and very tedious. However, despite these things, it is fun. Not like lounging on the beach fun, but it has some good moments.
I have learned that perseverance counts a lot in this field. You need to keep motivation despite the rejection you face on a daily basis. From agents, from your friends who don't write, from other writers keeping you down, etc. There are many obstacles you face and if you want to reach your goal, you need to break past them and make sure you keep focused.
This is hard sometimes with life things in general getting in the way. Carving out some time to write on a daily basis can be hard, but if you set aside an hour or two a day for yourself, you can reach your goal.
You have to be flexible and work around such obstacles, learn how bounce around without being stopped.
These are a little bit of the things that I have learned over the years. What are some of the things that you could add to this list? What things have you employed to get the time to write, schedules? Locking yourself in your room despite the distractions beating down the door? Have you ever wanted to quit so bad that you actually shut your computer off or set down the pen, vowing never to touch it again. yet come back to it later the same day or the next day? If so then you have the it factor, with a little luck and talent, you can make it. So keep going, if it's something you can't live without.