There is no rule that says we have to write stuff in order. It’s often easier, but it’s not compulsory.
Sometimes, if we get to a particularly sticky point, we may come to a shuddering halt. That’s bad for writing habits, where momentum is useful – it’s hard to get back into writing when you’ve taken too long off from it. Worse, if you find yourself blocked on a regular basis, you may find you start avoiding your project!
So why not write a different part instead?
That tricky bit can wait. You may even find inspiration strikes as you’re working elsewhere, or you discover that you don’t even need that scene in the first place. In the meantime, you’re still getting somewhere.
Just make sure you know where you got to.
The first draft of my unusual project, “Shuffle”, is now complete… and it changed a fair bit during the process. I wrote the last chapter just after the first one – and there are plot threads in it that have now been completely forgotten and no longer make sense. A rewrite will fix those!