I know, sort of vague headline, but that's because this isn't a Design Diary about any particular game, but games in general. Fantasy Flight sat down with some of their designers and asked them about their first designs they ever did, and ask about what they learned from those early creations.
From the post:
Even the most experienced game designers start somewhere. Before they worked on games like KeyForge and Arkham Horror: The Card Game, our designers began with their own amateur projects. For today's Designer Journal, we asked a few of them to tell us about one of the first games they ever designed, including how young they were when they made it, how the game worked, what inspired them, and what—in loving hindsight—was terrible about their earliest effort? Join us today as they tell us a little about their experiences as amateur game designers!