According to the Lexicon, motivation is a set of basic premises and values that move me into action. I consider myself an objectivist, and I recognize the fact that I have to work to live an independent life, but I have no motivation. I still do not know what I want to do for a career. I write things on my own time, but the goal of publishing a book or selling a screenplay is unrealistic. That is something I really want to do though, but everyone tells me it won't ever happen. I don't want to do anything else. In regards to writing something original, I am motivated. When it comes to my mom telling me to think "realistically" about my career, I cannot think of anything else I want to do. I wouldn't say I "refuse to think," but I will say that I think about refusing to pursue a career I don't want.
If I had to look at the situation from my mom's perspective, I'd have to say that the premise that she is acting on is that you should try to seek a job you enjoy, but you should take whatever job you have presented to you once you play your chips, even if you enjoy it or not.
UPDATE: She tells me that writing is a hobby, and that I need to pursue a career and learn a trade in college. I don't know what I want to do other than acquire a job in which I can write, and I have no interest in anything but politics, the economy, and cinematic entertainment. She tells me I'm going to end up being a Wall Street Protestor because I'm going to be a college graduate without a job. For the record, I would never go there to protest, and I completely disagree with that movement.
If you want inspiration, here's a true story.
A young foreign immigrant woman came to the US in 1926 at the age of 21. While her goal was to be a writer, she had to take odd jobs to pay for her basic living expenses. It took her almost a decade to finally get her works published/produced. Through her own efforts, she managed to adopt such a strong grasp of the English language that she wrote several books that have inspired millions of people. You can read more about her here
Lastly, I'll leave you with this quote:
"If you end up with a boring miserable life because you listened to your mom, your dad, your teacher, your priest, or some guy on television telling you how to do your shit, then you deserve it." — Frank Zappa