A helmet won't save you when you burn the tires, drive like a bat out of heck, blow stop signs, gun the bike, don't use your turn signals, fail to watch your rear views, fail to treat parked cars like a stick of dynamite, get yourself pegged in between traffic even at highway speeds, take highly travelled routes, fail to slow down for low visibility or blind corners/spots, jack your bike up so powerful that you can't stay off the throttle, ride without a windshield, go fast like cars do when it starts raining, fog up your helmet shield so you can't see, have a helmet where your hearing is muffled, having too heavy a helmet or one that doesn't fit correctly causing reduced speed of head motion and/or face slap, having a hyper passenger who can't remain still or seated, riding while on your prescribed medications, riding with too little sleep...
If you're guilty of some or many of those but wear a helmet, don't expect the helmet to save you.