In Duke Nukem Forever, Duke's "Health" is completely removed.
No longer will Duke scavenge medkits and armor scraps. No longer will being extra cautious in a tight spot help.
Instead, his very existence is powered by his own massive Ego.
A shotgun blast to Duke's face is nothing compared to the disgrace he just suffered from the scumbag who shot him.
Only a just and fatal retribution could bring Duke's spirits back up.
By pulverizing enemies, gallivanting with the local ladies, having happy thoughts or taking a leak, Duke can repair his broken Ego.
Even more than that, by displaying his skills without suffering a scratch in a lasting battle, Duke can boost his Ego to 200%, have an Ego trip and ALL BETS ARE OFF.
When ALL BETS ARE OFF, Duke enters a brief fifteen seconds of nigh-invulnerability, enhanced physical traits and infinite ammo.
A whirlwind of destruction and boot prints, Duke has a chance to lay waste to anything around him in any way he pleases.
Regular cannon fodder don't stand a chance against this self-absorbed Duke Nukem, but only Duke at his peak performance could stand against the baddest of the bad.