The Permanence of Snap Judgments
When I was in the eighth grade, my English teacher showed us a little psychology exercise to demonstrate the impact the order of adjectives can have on the meaning to a reader. I can't find it anywhere on the Internet, but I'll do my best to replicate it here.
Read this list of adjectives and decide whether you like the woman described:
Now read this one and do the same:
Most likely, you didn't like the first person, but you did the second. You imagined the first as a cold fish, but the second as an underdog. They're the exact same characteristics, but order is everything.
Once you get it in your head that the first character is "vain," all of the attributes after that are processed in a harsh light. You consider her intelligence and beauty negative traits that feed her arrogance. She probably only works hard for the money and status—a pointy-toed career women who would do anything to get ahead. "Shy" just seems like an excuse.
If you start out with shy and work backwards, however, a completely different picture emerges. You see someone nice and humble, who works hard to help others and make it in the cold, cruel world. Her beauty and intelligence are admirable, not alienating. And maybe she just seems "vain" to others because of her shyness, or it's a cute quirk that makes her more likeable because she's imperfect.
Snap judgments have a powerful effect on how people see and treat others. In real life, it can be mildly annoying. I've seen studies demonstrating that women will attribute characteristics to other women based on looks alone, before they've even met. Thin, pretty women are likely to be judged "bitchy" and held at arm's length. Large women are assumed to be lazy and dumb. The looks of the study participants had no effect on their tendencies; thin women thought other thin women were bitchy and plump women thought other plump women were slobs. Once you talk to a person for a few minutes, though, those judgments are usually replaced with opinions that have a little more substance. And if you get to know a person over a long period of time, your opinion should change slowly depending on how they act.
In writing, though, the first impression is everything. People will leap to the most distant conclusions based on the way a hero orders a footman to bring out his horse in the opening scene. They will do mental gymnastics to maintain their first impressions no matter what the hero does afterwards. If he was a jerk to the stable boy, when he says something dismissive to the heroine at their chance meeting, it's because he's an arrogant fool who doesn't deserve her. If he was kind, on the other hand, he's really a generous man at heart. His off-hand comment wasn't meant in malice, and she's at fault for misunderstanding and being bitchy about it. It doesn't matter if all men in the 1820s considered their stable boys a little below the level of sheep dogs. It doesn't matter how hard he tries to make it up to her. His character, and the reader's opinion of him, was already set on page one.
As disillusioned as I am with Jane Austen's skills as a writer, she has human nature pretty much down pat. Remember the twisted justifications and wild assumptions Elizabeth Bennet comes up with to continue hating Darcy and crushing on Wickham, long after it becomes clear that the latter is a cad and the former is just oblivious? On the first reading, if you don't know the plot second-hand, you should dislike Darcy too, and you only start to warm up to him when Jane cheats and shows his inner thoughts.
In Hollywood adaptations, the screenwriters and directors circumvent Lizzie's narrow viewpoint and make the audience cozy up to the hero right off the bat. They do this by showing close-ups of handsome actors with soft eyes, or by opening with dashing scenes of Misters Darcy and Bingley on horseback looking skillful and manly. In a two hour movie, they can't afford for the audience to hate the characters and realize their own prejudices slowly.
And unless you have the fame and fangirls of Jane Austen, most writers can't afford it, either. Potential customers make their decision to buy a book largely based on the first couple of pages shown in a preview. Even after they buy it, if they don't like the way it's going in the first few chapters, they'll stop reading and return it.
So what's a writer to do? Well, option one is to Pet the Dog. The basic principle is to convince the audience that your jerk-off hero is actually a softie deep down because he takes the time to feed the stray, rescue the frightened cat from the tree, etc. The pitfall of this is that, unless you choose an action that is sufficiently admirable, the reader can detect when he's being manipulated. Flipping a coin into a beggar's cup or holding the door open for an old lady does not get you a hundred extra karma points. One place I recently saw this fail spectacularly was in that Twilight ripoff I ranted about two weeks ago. After the heroine discovers her love interest is a vampire and freaks out, she hears him speak prettily about Keats. Then all of her doubts fall away instantly because, and I quote, "I don't think anyone who talks about the Romantic poets the way you do could hurt anyone." I know of a local man who was raped by an English professor and might argue to the contrary.
The other option is, as I did with the lists, to hold off on the negative traits until the positive ones have already taken root. This is what I'm doing with Leo in the new revision of WIP-B. He's still an immature idiot, but I don't reveal that tidbit until after I've established him to be, as Sweetie put it, "a joke character." If your heroine is sweet and playful, once she starts acting up it's because she's "misguided." If she starts out selfish, however, when she cracks jokes it's "annoying" and when she reveals her soft side it's "unconvincing."
Keep in mind that the gender of your characters has a lot to do with the way readers perceive them. Consider how differently those lists would read if I replaced "beautiful" with "handsome." Then the first list would represent an alpha male, and the second a Joe Schmoe. You can get away with a hero who's cold, intelligent, and a touch arrogant or even downright mean. But that same mix in a female is the kiss of death. A bastard can be reformed once the merciful heroine scrubs away his rough exterior to reveal a shining heart of gold; a bitch is just a bitch.
Similarly, a man who sits back and does nothing when evils are afoot is weak. A woman who does the same is a damsel in distress. Remember, Men Act, Women Are. This is actually powerful enough to subvert any unlikeable traits you give your characters. A vicious woman, if she's a victim, is alright (*cough* Lisbeth Salander *cough*...See also: Double Standard Abuse). And an evil SOB, if he leaps into action to save the day, morphs into a badass. Should you use the trope to manipulate your readers' loyalties? No, not if you have a conscience. But an alarming number of modern writers do, and it works...at least commercially.