The hardest part of a story to write.

The hardest part of writing a story is getting past that second chapter. A lot of people can write the first chapter with no problems, but when it comes to the second chapter, people tend to put it off.
The best thing to do when this happens is to move on to a different project until you feel that you can write the second chapter, that way you are still being productive.

The first couple of chapters are the hardest to write. It's always difficult to establish the story because you're literally starting something from nothing. You need to make the readers care about the characters, the setting, and what's going on all in the beginning to give them a reason to keep reading. But once you get past that part it gets easier in my opinion. But I wouldn't suggest putting it off. In some ways, the beginning of your novel is the most important part of the story, so it's something that should warrant most of your effort. No matter how long it takes, get those first few chapters down. After all, if there ends up being anything you don't like about them you can always fix them up later.

Depends on your writing style. I know a few people who just write for fun and jump between projects whenever one gets tricky, and others who are rather stubborn in their dedication to one story. The latter is often preferred if you're trying to get published.

But I wouldn't really give up on the second chapter. I'd probably think about what could happen next and how to bridge the gap between where you want to be and where you currently are. Chances are you already have an idea of where you want to be; for me half the fun is figuring out how to get there from where I want to start. Just let the plot sit on the back burner of your mind when you figure it out.

The beginning is usually the hardest? Wow... I'm really envious of those people. I find the part directly after the narrative hook to be difficult. That transition from the first scene to the rest can be brutal. Of course, the problem is that I've always switched styles from my usual horror to... well, something else. One hint that I wish I had followed is to make sure what comes next. You don't have to know everything, but at least have something to work toward. Also, if writing without a definite plan, give a character some really strange line or interaction and then go back to that later.