I like collecting advice from other writers. One thing that has stuck with me is to expect rejection. And now that I've emailed off my proposals, that's what I'm doing.
Now, don't get all Pollyanna on me and tell me I need to believe in my dreams. People who believe in dreams are most often delusional.
The standard answer to a query or a proposal is a "no." That is, if you even get an answer at all. To not know that is to set yourself up for disappointment and dejection from the beginning.
While there are an endless variety of attitudes aspiring writers can have, ranging from the Eyorian hack(It ain't never going to happen) to the Disneyesque pre-published (believe in yourself, and all your dreams will come true), I probably fall somewhere in the mucky middle of realism.
New authors get published all the time.
Most manuscripts are rejected.
Balancing these two is perhaps the healthiest medium for me.
Writing is a lot like a lottery in that, the odds are slim.
Writing is unlike the lottery in that, you can change the odds. Honing craft, and working and editing the manuscript take time, but also yield results. Preparing a professional query/pitch/proposal also ups the odds.
But even so, there are still so many factors the writer cannot control.
You cannot control the economy, and how many other books are competing for fewer slots the publisher is trying to fill.
You cannot control the market and which genres and trends are likely to sell.
You cannot control the subjective response of the reader. What one agent or editor might love, another might hate.
And you cannot control the competition. Even if you produce a great manuscript, you will always run the risk of someone popping in with an even better one.
So what is the aspiring writer to do? Keep plugging away. Don't think of being published as the only end to your writing. Consider it a bonus--a distinct, but distant possibility. Keep your feet grounded in reality, and work toward your dreams.
But never give up your day job.