But let’s say that you feel you need to drop some information to the audience that they’ll need later, so you have somebody casually mention something important in conversation with the hero, but the hero doesn’t notice or care, even though it should be a big clue... This is a huge sympathy killer. If you’re hero passively receives an incomplete piece of important information and doesn’t follow up, then the audience feels betrayed. They say to your hero, “Hey, loser, I’m counting on you to dig up all the information I need to enjoy this story, but you’re not asking the follow-up question I need you to ask! What good are you?”
Now of course, you can occasionally have your hero “miss” a piece of key info that the audience picks up on, but only if the audience feels that the hero has a good reason for missing it, like a big distraction. Even better, drop the information, then have the hero and audience both get distracted by something else at the same time, so that they both forget about it. Then, later, when it turns out to be important, they’ll both be kicking themselves at the same time, and they’ll bond even more.
It’s an equally big sympathy killer if heroes don’t act on the concrete information that they do receive. This can be a problem when you try to build tension by ending every scene on an ominous warning of some kind. Oooh- spooky! But then, in the next scene, the hero has moved on to another part of their day, and they forget all about the warning until it’s too late, three scenes later. You can make a case that not every hero has to be proactive, but at the very least, they have to be reactive.
The audience is constantly trying to anticipate what’s going to happen next. If they can tell that the hero is not able, or not even trying, to anticipate a consequence that we can anticipate, just by looking over their shoulder, we feel powerless. Why are we putting our trust in these schmucks?? Remember on “The X-Files”, when they would get a big piece of the alien invasion puzzle at the end of an episode, and we’d all be on the edge of our seats, and then next week they were back in some podunk solving some dinky little monster mystery, as if they’d never gotten that big clue? Remember how infuriating that was? Don’t do that.