Foreground growth seeks to subvert the abstract style of class advancement you get in D&D. Instead of a magical metamorphosis occurring in downtime, development of your character is based on events in-play. For any character ability, players should be able to relay a story from a game session that explains its origin.
There is a good illustration of this in Cairn’s FAQs, in an extended descriptive example of gameplay. An unexpected encounter with a patch of bioluminescent water leaves a character with a foot that glows in the dark. This somewhat dubious ability isn’t found in a shopping list at the back of Cairn’s rule book, but emerges in the context of an adventure.
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| Fear my glowing leg |