You're nearing the end of a grueling battle, and things are looking grim. Your health packs are depleted, your comrades are down for the count, and you're on your last legs. The boss is close too, at the end of their humungous health bar, and if you drop now all that effort will be wasted. So you go in guns blazing, throwing out every ounce of firepower you've got in a screaming hellfire assault (or hiding behind a box and taking potshots, whatever), and after several pulse-pounding moments the boss drops dead, with you a strong sneeze away from death yourself.
The elation of victory that hits you in that moment is something that can't be artificially replicated. As hard as developers may try, the intersection of desperation, skill, and luck that makes that happen isn't something that can be prearranged without losing its magic. It's all on you, and when you beat a boss to that final punch it feels like you're Bruce Willis for a good minute--which is a week's worth of victory in regular-person years.