Preferences, everypony has them. These preferences mould us, define us into who we are in the present. Sometimes, our preferences seem to be decided for us, not discovered, this seems to be the case for young alicorn Twilight Sparkle.
It had been 2 years since Twilight loved to Ponyville, 2 years since Princess Luna's first Nightmare Night, 2 years since the seeds of Twilight's love for Luna was set in the soil.