Leverage is a unique stat that specifically deals with interacting with another character, player or non. Are you helping someone? Trying to stop them? These are the two main situations when you will roll Leverage. Every character has a different leverage score for every other player character and any NPCs added to the party, which are noted on the character sheet.
While the other stats are set at the beginning of the game and don’t change, Leverage changes as your relationships with other characters change. Every time a player has their character interact with yours and do something that strongly aligns with their virtue, they may increase their Leverage for that character by 1 (max of +3). If that character does something in an interaction that really doesn’t jive with a virtue, they may decrease their Leverage for that character by 1 (max of -3).
+Leverage determines how characters can help or hinder others, whether the others are player characters or NPCs. For those other characters that one has a positive relationship with, helping or hindering them will be much more likely to be successful than not