I'll try to avoid Dracula-posting too much over here, but I would like to point out that, while Jonathan Harker is often teased for obliviously wandering into the jaws of death, he understood that the Vibes were Off enough to preemptively wish Mina goodbye on day 2. And this is before, well, tomorrow.
Like, he has zero context for supernatural stuff being a thing, of course he wouldn't give up a business trip over what he currently considers to be superstition. He also doesn't know yet that the superstition is about his client being Definitely Not a Vampire. But he is worried, and I would argue that this all sets him up to survive Castle Dracula--because he's going into it already feeling that, generally, things are Weird, so he's quicker to pick up on and observe odd things.
