I had a plan for dinner. I got out everything I needed. Preheated the oven. Reread the recipe. Ready to get it done and provide a yummy meal for my family, I set about the task with zeal... so much zeal that I sliced a chunk out of my thumb on the mandolin. Blood gushing and my dominant hand now, well, unsanitary and out of service, my plan changed entirely.
If you're grappling with a scene that doesn't seem to be going anywhere, throw in a little accident. Just because you and your character make plans doesn't mean they'll be carried through the way you expect.
Divert your scene with a little accident and see what happens.