Writer's Block

I sat down to write today and realized there are parts in my plot I want so badly to make sense. But they don't. I want them to happen. But it's not logical that they should.

I need some strong plot devices to motivate my characters and move them to do what I want.

What are your favorite plot devices? How do you get your characters to do what you want them to?

Also, it's been awhile so here's a new Metaphor of the Day Assignment:

Write a metaphor that describes either a pleasant or unpleasant aspect of your main character.

Example: (Highlight the text below if you need inspiration)

(Note: these are about two different characters)

She was as thin as a sickly piece of grass. Even her complexion looked green and tender.

or

The herbalist was a flower herself: she bloomed where she planted and looked after her own.