My understanding is it's not a trigger for lucidity, but a confirmation you're lucid in a dream. I had my first LD Thursday and prior to checking my hands I possessed some level of waking awareness and that I was in a dream. The RC only confirmed what I already suspected.

So working on awareness in waking life allowed some level of waking awareness to arise in my dream, and that waking awareness knew it was time to do a RC for confirmation of my state.