960 Altered tactics in French and Slav formations
At starting position #518, the phrase I keep repeating is "use inactive force". At the other 959 starting positions, I recite "it's just chess". The pawn structures recur from Schnargl (a code to identify a starting position) to Schnargl, so do the strategies and tactics(which means the secret at chess960 is "use inactive force").
While the structures, strategies, and tactics are shared across all 960 Schnargls, the thing that makes chess960 unique is that the same old tactics spring from unexpected places.