Saturday, August 10. 10:00 AM. I’m sitting in an expo hall, behind a table draped in black cloth and decorated with some of my recent LEGO creations. But they’re not what’s capturing my attention. Instead, I’m staring at a box awkwardly wrapped in fading purple construction paper and wondering what it conceals–and knowing that whatever it conceals will haunt my days and dreams for the next two weeks.

I was invited to participate in Iron Builder–the toughest LEGO competition out there,...