As Chris wrote in No Plot? No Problem! (the Bible of NaNoWriMo), if you want to put the ninjas in the courtroom scene, goshdarnit, put those ninjas in there.
Ninjas, for me, serve a different purpose. Whenever I get stuck (that is, five or six times during a writing session) it's because I'm bored. Boyfriend/girlfriend conflict, parents screaming, friends talking... my attention then begins to wander and I'm stuck two pages behind my goal.
Then I immediately think "ninja."
The theory behind this is that if I put a ninja in my book, it would immediately be more interesting. Who is the ninja? What is he doing in my book? What will he do? What if it's a she? Is she a feminist ninja? How will my characters react to a feminist ninja? Will they throw a rally?
My Bestselling Author self looks at these questions and sighs. No, I cannot throw a ninja into my novel about high schoolers in an overachieving Virginian school... but I could throw in--
And that is why the key word is always ninja.