In a game as sustained and brutal as Dark Souls 3, victories tend to be small and short-lived. But those moments, when they present themselves, are as sweet as they come.
It’s part of the reason why From Software games are so compelling. Rewards are sparing. Rewards come with a real sense of achievement.
I believe there are roughly five different emotions you feel upon defeating a boss in a From Software game, ranging from white-hot rage, to zen-like satisfaction, all the way to a low level thrum of disappointment. It all depends on the difficulty and how you finally dispatch of the boss itself. It differs from person to person, from boss to boss.