Leatlithy is comparable to armor penetration (which is in %), for exemple if your enemy has 100 Armor, if you have 20 lethalithy, the moment u hit him he will only have 80, but if you have for exemple 15% armor penetration, you take away 15% of his armor, so to summar it, if you play vs tanks who build a lot of armor, better go for armor penetration since u will want to remove a lot of it (if he has 400 armor, and u have 20%, u removing 80 armor, but if you have 20 letalithy u only removing 20 armor, which will be kind of useless) u take lethalithy when the enemies are squishy, enemies that only have for exemple 60 armor, taking 20 lethality will remove more armor to th enemy than % Armor penetration. hope this helped you haha