You start writing, and things go well for a while. You establish characters, and the story begins to unfold nicely. Then suddenly you hit a knot. An action that has to happen doesn't make sense for a character, or an event that has to occur isn't likely in the scenario you've created. What do you do?
Some writers outline their stories carefully before they begin writing, and I suppose that eliminates a lot of plot-knots. I can't do it. I never liked connect-the-dots; I'm a pantser whose characters make their own story. That means that I get more plot-knots than some, but it's the way I like to write.
So what do I do? First I take a long walk. Minor knots usually work themselves out with just time away. For bigger problems, that may not work. For example, recently I've had this knot to work on: a civil war is coming. One secondary character will have to choose sides. If he chooses the one that is more logical, it would set him against my protagonist, which I don't want. If he chooses the other side, however, he'd be a traitor to his own people. Hmmm. The whole traitor thing might work in a more tragic work, but that's a bit heavy for my genre.
What I've done is write past it, getting the story told and leaving the secondary guy sort of on the edges. As of yesterday I think I've got the problem solved, but it will require some rewriting. If you read last week's entries, you know I do a lot of that anyway, so it's okay.
What you can't do is stop writing and wait for inspiration. That is how manuscripts never get finished, and I know LOTS of authors who've let themselves be frozen by indecision. Write something, even if it's wrong. Bernard Cornwell compares it to climbing a mountain. You can't see the whole path at the beginning, so you may go off in a wrong direction. Suddenly you come to an open spot and you see your mistake. Still, from there you can see where you've been, where you went wrong, and where you need to go. It's not a wasted trip because you gained a better view of the journey.
Solving plot-knots is mostly not giving up. Your first solution may be ridiculous, unwieldy, or just plain wrong, but let it go for a while. (Don't leave it, though, and assume the reader won't care!) Write past it and then let it sit; better solutions will occur to you. Yes, that involves re-writing, but hey, isn't that what you are? A writer?