Handling "that difficult chapter"?

I've just written a couple of very difficult chapters, which got me thinking - what makes a chapter difficult? Obviously there are a lot of possible reasons why a chapter might be hard, but here are some:

1. You don't know what is supposed to go in it.
Maybe you're riding the momentum of the previous chapter, but then that chapter ends and you don't know what to do next. That might be a good time to go back and look at the arcs you have established in the previous chapter, or in the previous two chapters. Those are generally things that you'll want to pick up and continue as you go forward. Knowing what your basic arcs are can give you a backbone for a new chapter that you can then flesh out as you go.

2. You know a bunch of stuff that goes in it, but it all seems to happen without any trajectory.
It sounds like you haven't found the core of the chapter - the thing that happens in the chapter that really matters to the main conflict. If you're writing and it feels like every event that happens has the same importance as every other, then maybe you're not understanding the importance of one of the events (how that event contributes to change in your protagonist, for example) or you may even be missing a critical event. This happened to me in my last chapter, because I didn't realize that Tagret had to confront each of his parents about his brother's mental illness. Once I put that critical piece in, the other things in the chapter provided the perfect background and lead-in to it.

3. What happens in the chapter upsets you.
I had this problem in my last two chapters, for two totally different reasons. One was a situation where my servant character was watching his mistress get hurt by the bad guy and couldn't do anything about it. The other was a situation where my protagonist woke up from nearly dying and got really, really bad news. Let me begin by saying that this was what had to happen. If your chapter content is upsetting you, don't retreat from it. Think about how to handle it, sure, but don't run away, or the story will be weaker. My recommendation for this is to do it in small doses. I actually had to use the "battering ram technique" - writing along until I couldn't stand it, then backing off, reading up to that point again, and seeing if I could make a few sentences' headway until I couldn't stand it again. Then backing off for a break before returning and reading back up to that point again for another sentence or two of headway until I broke through.

There are other problems that can happen with difficult chapters, but I hope these suggestions can give you some ideas about handling some of them.