This was a phenomenally terrible plan because I had yet to fully understand the correlation between my state of mind and the strength of the magic. Fear that I had hurt Luna, frustration from being unable to help a single person today, and that feeling of impotence from being unable to control my own powers created a nice, hot cup of resentment that my horn greedily slurped up. And with the guards egging me on, it was only a matter of time before something had to give. And when the rock finally gave, with all that built-up energy, it gave hard.