Why is it that when you have a character design in your head and then you draw them out, their appearance changes?

Like for Isa, I modeled her, but chose not to put the dragon birthmark on her face (at the moment), as it was hard enough to put the Triforce (it's a contract, not an actual Triforce) on her. Granted, she doesn't show her birthmark all the time.... And I modeled her form when she meets the Voltron crew...

As for Chris, I modeled her as well, then threw glasses on her on a whim. Now I want her to have glasses in her story because she looks good in them, so I'll have to write them in. Also, they happen to be Bayonetta's from Bayonetta 2.

Oh, and neither of them have shoes. I'm lazy that way, plus a lot of shoes have heels, and neither girl wears heels. Alicia, maybe, but not them.

Now some facts about the girls:

Fun fact #1: Someone who read Nintendo Nightmares asked if Chris was going to be an Umbran Witch, and now Chris has Umbran glasses. This was a coincidence... Kind of.

Fun fact #2: No matter what happens, Isa always changes. The one constant is that she goes by Isa.

Fun fact #3: I never really describe Chris outside of her night shift uniform.

Fun fact #4: Isa was supposed to be a shinigami. Then a pop star. Then a vessel for possession. Then a mercenary. Then an otaku. Then a student. Now she's a tech and -//slapped

Fun Fact # 5: I wanna include Chris and Isa in the same story. One idea was for Isa to pop into Nintendo Nightmares, but it was scrapped within a few days. Now the idea is that either Chris (as an Umbran Witch) and Isa (after spending time in The Vampire's Servant) cross paths in Paradiso or something, or that Isa and Chris get sucked into an alternate world, and Chris is a mere mechanic, while Isa hasn't lost her sanity yet. Anabiel, Reiko, and Alicia woulf have made an appearance as well.

Or even yet, I could write a story where they live in the same world, with Chris leaving outside of a special city, super poor and making stuff. Isa, someone who once lived inside the special city but is a fugitive, and crashes in front of Chris's house, wounded. Alicia is the princess, Anabiel is an assassin, and Reiko lives in another country. Or something. I might include Nico and Asa as well.

Just a thought though. Still working on that Tharja Death Note one-shot, as I'm trying to make Tharja.... Tharja.