There are some classes of potential Steam achievement that a player could get by accident either through modding or just playing the vanilla game with unusual embarks/adventurers, and thus they might feel disappointed like "oh man I didn't earn this, it was too easy" when for example, they earned the achievement for "become legendary at a skill" because they played as a barn owl man that [NATURAL_SKILL:CLIMBING:15]. Or maybe a hypothetical achievement for managing to survive X years even if you embarked without food or drink, obtained by accident because they played as a species with [NO_EAT][NO_DRINK].
So basically, when writing achievements, consider some of the ways that through modding, or future game updates with more procedural content, or even the current vanilla raws (so many animal people are legendary climbers!), someone could plausibly gain them by accident, and do some sanity checks before granting the achievement to prevent this.
Such checks should be used carefully/sparingly though; for example, an achievement for stopping an invasion shouldn't be invalidated just because your species has good NATURAL_SKILL's that gave you an edge. Sure, someone motivated to deliberately cheat could give themselves inflated skills and tissues made of iron, but they could also use third-party tools to command the Steam server to grant them achievements for free (ie call the server and make it think you earned it genuinely). The goal of what I'm proposing isn't to stop cheating (that would be impossible anyway, there's always a way), the goal is to stop people feeling cheated by accidentally getting achievements that were meant to be a challenge.