A friend of mine told me a bad joke once:
What's worse than finding a band-aid in your hamburger? The Holocaust.What's the worst that can happen? is probably the most-recited piece of advice on plotting. It's good advice, and I'm a big fan, but as the joke illustrates, "worst" is very subjective.
Take this scene. Your protagonist is upstairs, and she hears a noise downstairs. She grabs the bat from under her bed and goes to investigate. What happens?
A) She finds a burglar in the living room stealing the silver.
B) A sinkhole has opened up under her house and it's starting to collapse.
C) The sun explodes, killing all life on Earth.
Obviously, "worst" has many outcomes, and not all of them are going to work for your story. My examples are extreme, but we pick the metaphoric C more often than not, because it's "the worst that can happen." We're thinking about how to make the plot bigger and badder, not always what's the best "worst" for the story as a whole. And that can lead to scenes that might be exciting, but our beta readers are giving us feedback like "but it never goes anywhere" or "yeah, it's good, but what's the point?"
Things going wrong are vital to a good plot, but you want to look for things that can go wrong and still move the story forward, and deepen that story while they do it. Connect the "worst" to the story so it keeps the reader interested, and doesn't just give them stuff they have to slog through to get to the next story point (even if that stuff is interesting on its own)
Instead, try asking...
1. What's the worst thing my protagonist thinks might happen in this scene?
Odds are your protagonist went into this scene with a certain amount of apprehension. (If not, that's a whole other post) What are they worried about? What realistic fears and unrealistic fears do they have? Don't just look at the most immediate fears. Look at those inner fears, childhood fears, etc. (Can you say "character arc" anyone?) What do those smaller fears mean to a bigger problem? Brides worry about tripping on their wedding dresses, but it's not the "falling and getting hurt" consequence that scares them. It's ruining what's supposed to be the happiest most perfect day of their lives and haunting them for the entire marriage. Or even being a bad omen that the marriage isn't going to work out, preying on a deeper fear they might not be willing to face.
2. What's the worst thing the other characters in the scene think might happen?
This includes bad guys. Your protagonist may be driving the story, but it doesn't have to be all them all the time. Another character can offer you inspiration on what to do next in your plot. Bad guys often have more knowledge about something in a scene (because the protagonist is probably trying to find that secret out), so they'd react to things from a different perspective. To them, the protagonist getting to X might be the worst thing. And then they'll act in a way to prevent that, which could cause just the right problem for your hero.
Looking at the other characters is also a good way to keep the reader guessing. If the protagonist has been worrying abut X, the reader will suspect X is going to happen. But they probably aren't expecting Y. And a secondary character, might be worried about Y, which might cause just as much trouble for the protagonist as X. That also provides opportunities for other characters to get a little page time and become richer characters.
3. What the worst thing the author thinks might happen in this scene?
Don't count yourself out. This is a great time to brainstorm. Take a step back and look at this scene as if no other existed (Yes, I know, this goes against that whole "make them connect" advice, but bear with me). What problems might develop from this situation? Look at all sides, minor and major characters, setting, theme, let your mind wander. Think about later in the story. Is there anything that could be made worse there if things turn out differently here? What would totally kill your plot if it happened? Now, how might you get out of that if you actually had that happen?
In all of these questions, don't think, "I can't do that because..." Think about how you would handle it and see if you can pull it off. Because the last thing you would do, is probably also the last thing your readers will expect.
How often do you choose the worst that can happen in your plots?