^Again, don't fixate on a single idea. Ideas are the easy part. What matters is the execution. You need to give them the best work, both in concept and execution, that you're capable of.
So don't think of an idea as "second best" just because it isn't your personal dream. Instead, find another idea that fits the parameters and inspires you just as much, and put as much care and effort into it as you would put into your dream idea. Remember, this isn't a hobby. This isn't an exercise in personal gratification. This is a job
. If you're applying for a job, you need to show your prospective employer that you're committed to doing your best possible work no matter what they assign you.
And if you look beyond that one single idea and see what else is in you creatively, you may be surprised at just how much is there. You may find better ideas that hadn't even occurred to you because you were spending all your time thinking about just one idea. You may discover a new idea that you want to do even more than this current dream idea of yours.
Years ago, I had an idea for a trilogy I wanted to do about Picard's missing years between the Stargazer
and the Enterprise
. When Marco Palmieri invited me to do the Lost Era
novel doing just that, naturally my first thought was to do the story I'd originally planned. But when I took a close look at it, I realized it wouldn't work. And then I came up with something that turned out to be far, far better. I got to do my dream story, but in a totally different, much more satisfying way than I'd originally imagined.
So just because there's one idea you really want to do now, don't assume it's your "best" idea. If you really have what it takes to be a writer, and are willing to do the hard work to make it happen, then your best ideas are still ahead of you.