When one is an author it is necessary to have characters and possibly Loads And Loads Of Characters. To effectively write these characters you need to be empathic to them; to know their personality and mindset. This will enable you to write actions that are true to their character. The trick is that these actions may seem illogical to you personally, but make sense to the character.
I often see a lack of empathy on Tvtropes. Tropers passing judgement on characters for being stupid or whatever. The problem is, they're doing this from their own mindset and their own prespective. This leads to a dissonance because the character's actions make sense to them (and their writer) but they don't make sense to the Tvtroper.
There's a quote from Tolkien's The Hobbit that directly addresses this. It's during Biblo's riddle game with Gollum. It goes along the lines of "It is easy for you, sitting in your room, to answer these riddles but for Bilbo" it is more diffcult. Bilbo is alone, in a dark cave, far from from home and right next to a creature that's moments away from eating him. The person reading The Hobbit is likely doing so in more comfortable/less threatening circumstances. Thus, Bilbo will reasonably have a harder time thinking straight and thus solving the riddles (and coming up with new ones) than the reader.
There's also a scene from the X-Men film series. In "First Class" Charles tries to convince Erik to show mecy to their enemies by saying that they're "just following orders". For a holocaust survivor, this is not a valid argument, to say the least. A viewer is left wondering, if Charles is such a highly educated man, telepathically picked Erik's life history out of his mind earlier in the film, and has shown great insight and ability to get along with others in the movie, why does he make such a blunder? I read the answer on Tvtropes.
As much as it has bitching and complaining, it also possesses a hoard of insight into characters because many tropes demonstrate this kind of empathy. They figure out why the characters do the things they do. The answer in this case is because Erik is wearing an anti-telepathy helmet. Charles has been a telepath since he was nine and so he grew up with this power. It's how he relates to others and now, for the first time in his life, it's unavaliable. It's like blindfolding someone and asking them to move around in their home. They may have lived in it for years, but without their sight, they stumble because they're not used to the sensory deprivation. This is ontop of the high stress situation and a tremendously painful experience Charles went through moments prior (anyone else who has seen the movie knows what I'm talking about). Thus, he blunders and viewers call him an idiot and other things.
You might be thinking-what's the point? If the characters acting in character means my reader can't relate to them, then shouldn't I avoid that? After all, if they can't identify with these characters, then surely no one will read my book! No, you shouldn't dismiss character empathy and especially not for some fool's errand as "character identification". If characters don't act in character than you don't have characters. What you have are puppets for an invisible puppeteer (i.e. the author). This is worse.
For one thing it ruins immersion. If characters don't act like real people (or as they are presented) then the reader is reminded that they are not real and the situation is not real. This can cause them to stop caring and Tvtropes calls that scenario Eight Deadly Words because the reader has lost interest in your work.
For a second thing, if characters are not driving your plot then your plot is driving your characters. This leads to all sorts of bad stuff like As Strong As They Need To Be, Character Derailment, Idiot Ball, Poor Communication Kills, etc. It's snark bait. I've seen on twitter, on tvtropes and in other places.
Finally, why character identification is a fool's errand. Even if you were writing for a single person, and based a character on them, they might miss it. They could instead look to another character. Now consider an audience that could be thousands of more. Their opinions will be as scattered as the stars in the sky. Furthermore, you could write to group A but misinterpret and offend; you could instead attract group B and be unaware of this. By making someone identifiable, you do harm to your characters and leave out parts of your audience. It's best to focus on your characters and making them the best they can be then trying to guess your audience.
The characters must act consistently and to do that you as an author need empathy for them.