Sekiro: Shadows Die Twice is a difficult game. That should be expected though as a From Software title, the makers of Dark Souls and Bloodborne.
Given Sekiros steep difficulty, it might surprise you that speedrunners are already beating the game in under an hour. In fact, the world record was set last night when speedrunner LostFeather beat the game in 39 minutes and 13 seconds.
Source: N4G PC Speedrunner beats Sekiro in under 40 minutes