Toughness is a new gameplay stat added in The Lost and Damned. It is basically the combat skill level of fellow members of The Lost Brotherhood who travel with Johnny Klebitz, to include Jim Fitzgerald, Clay Simons, and Terry Thorpe.
Once you achieve 100% Toughness with all your fellow members, Terry is armed with a Carbine Rifle and an Micro Uzi (for Drive bys), Clay is armed with an Assault Shotgun, and Molotov Cocktails, Jim will have an AK-47, and non-storyline characters will be armed with AK-47s and Molotov Cocktails/Uzis.
The player can also gain Toughness for his Backup (Terry and Clay) in other missions during normal gameplay. Some missions have two different paths of completion, one without Terry and Clay's interference and one with them as backup.
Non-storyline brothers who die in the campaigns will be in memorial in The Lost Clubhouse, with a photo and a gravestone. They will be replaced by a new active member and have their toughness score reset.