Some don't seem to realize that bestselling authors represent only a small percentage of working writers. (Though, as an aside, I do wonder what Stephen King's first advance was....) Based on some of the first-timer queries I get, it also seems there are a number of people who don't realize how competitive the field is for becoming published in the first place, and how much more likely it is to get a $5,000-$10,000 advance for a debut than a six-figure deal. One should also note that not every book published gets made into a blockbuster movie.
It's too bad this perception can set up unrealistic expectations for getting started and building a career in writing. But it seems prevalent from a number of different perspectives. So many writers who have garnered that first contract offer mention that they were immediately asked by family and/or friends -- or even people they were only marginally acquainted with -- how much they made (is it rude to ask?) and when they'd be sharing the wealth. Like they've won the lottery or something.
My favorite was a recent email I received from a real estate agent. I have no idea where they found my email address or what possessed them to contact me. They were asking me to let my clients know about a property they had for sale - a mountaintop retreat that would permit my client to work in peace and solitude. How much was this gem listed for? 2 1/4 million dollars.