I first became aware of authorial bleed through a decade or so ago, when I was workshopping an (ultimately trunked) short story about a guy named Jim, whose best friend Dave essentially fell in love and ran off with the king of Elfland's daughter the night before their college graduation, without so much as a goodbye to Dave or anyone else. In the aftermath of Dave's disappearance, Jim stayed up all night with another friend of Sarah, "over cups of stale tea, neither of them speaking." Sarah had been Dave's friend, too, so she and Jim were both pretty shell-shocked by his departure.
Anyway, I'd been through this story quite a few times by the time a critiquer finally said to me, "Tea? Wouldn't they be drinking something, umm, stronger?" When your best friend runs away to Elfland without leaving behind a forwarding address, isn't your first impulse to get drunk as hard and as fast as you can?
This had honestly never occurred to me, and it took me a few moments to realize why--it was because my impulse wouldn't have been to get drunk. My impulse, especially at the time I wrote the story, would have been to consume large quantities of tea without speaking a word, because I don't actually don't drink much alcohol. So the possibility that many characters--maybe most characters--would be downing shots instead hadn't even crossed my mind.
Now, it's possible that Jim isn't like most characters either; that his drinking tea was meant as a deliberate act of characterization. But I gave the story a good hard look, and I knew this wasn't true. Jim was precisely the sort of character who would get drunk the night his best friend ran away to Elfland--because he was a reality-avoiding sort of guy. If he hadn't been, he might have noticed his best friend acting a bit strange, in the weeks before graduation; he also probably wouldn't have hung on to his student apartment and continued living--and working--near campus for years afterwards. This is not a character who faces cold, hard truths head-on.
In other words, Jim drank cups of cold, stale tea for no better reason than that his author drank tea. (Hot, not cold and stale; but then, I've not yet lost any dear friends to Elfland.) My own preferences were bleeding through.
Once I allowed Jim to be true to his own (inebriated) nature, other plot pieces fell into places as well. For one thing, I realized that, if Jim--and Sarah--got drunk that night, there was a good chance they would wind up sleeping together; and that if they did, this would fuel the second half of the story, which takes place five years later, when Jim is still living in that apartment, and Sarah--who he's hardly spoken to during that time--comes back for their college reunion.
I got distracted and never actually finished that rewrite, probably because Jim's choice of comfort beverage wasn't the only problem with the story; though it is still in my file of stories to return to one day. But the point is, to even start rewriting, I had to get over my own unconscious preferences and biases, and find the preferences and biases specific to my character. Until I set him free to be himself, and not a reflection of his author, the story had a certain air of self-indulgence, and a certain lack of tension, too. And the story, well, just didn't work.
So now when I read a book where the characters have desires or preferences that just don't fit--especially characters in other worlds and other cultures whose views seem overly informed by our world--I wonder. Is the character doing and thinking these things, or is the author?
And when my own characters have a habit or quirk that doesn't seem quite right--or even that I'm just a bit too fond of--I ask myself the same thing.