There is no one with whom you are going to be compared, or 'accused' of trying to emulate, or be told 'so and so did that much better', no one to tell you that this is 'the' way in which the characters should/must be written, etc. etc. etc. You can form your own view of the characters based on factual and interpretative canon, and they are 'yours'. You don't worry that maybe you've been influenced by other writers.
Also, you learn about the characters and discover bits and pieces as you go along. You don't get it all in one sitting. You are limited to the amount of new episodes you can see by virtue of the TV stations. In many ways it's like a relationship.
So you go along and form your own universe that is based on both factual and interpretative canon, and you are happily ensconced in this world, adapting as you go along, if you have to, working new information into your characters and stories. And everything is comfortable and nice.
And then out of the blue one line, yes, one line can completely if not shatter your universe, can at least dent it. This happened to me last night when I watched the first part of Hiatus. I won't go into detail here, as I'm sure that those of you who are really interested have already read my review over on ncis_gibbsducky. But if you are interested and don't mind spoilers, then it can be found here. But be warned, it does contain spoilers.
I loved the episode, it was so powerful, so intense, so wow! One of the best of what I personally consider to be a fairly mediocre season (certainly when compared with the previous two). However, this one line did trouble me somewhat. And as the evening wore on the 'somewhat' moved into something much more. It's safe to say that whilst it didn't quite keep me awake, I clearly didn't rest all that well, as my mind churned and mulled. (Note to self: am I really that obsessed?)
So this morning I did what any respectable fanfic writer does, I wrote a story, because after all one of the purposes of fanfic is the 'fix' canon whilst working within it, isn't it? So I'm happier now as to my mind the story I've written (not yet posted, but later today or tomorrow) solves my 'problems', but still fits in with the existing canon, as well as the new information. And I hope (fingers and everything else crossed) is open enough not to be contradicted by anything that might happen in Part 2 (spoilers for which I am still avoiding and intend to go on doing.)