I spent the better part of my twenties thinking my body was unpredictable. One week sharp and focused, the next week foggy and tender — craving different food, needing more sleep, finding the same social situation that felt easy a fortnight ago now unexpectedly exhausting. It took years before I understood that what I was experiencing was not randomness. It was a programme. A 28-day biological programme that was running, flawlessly, every single month. Nobody gave me a map. So I built one.