I’ve learned a lot every time I’ve done public speaking, but this time I picked up a specific, tactical lesson: empty your back pockets before getting on stage. About fifteen minutes before showtime, I took a hairbrush to the bathroom to fix up my hair, stashed the brush in my back pocket, and then immediately forgot about it. The time I spent preparing and practicing doesn’t matter — the demo gods have enacted their revenge for my talk not actually including a demo.