Why is Sekiro so hard?

Could you elaborate on why Sekiro: Shadows Die Twice is considered a challenging game? Do its combat mechanics, level design, or enemy AI pose a significant obstacle for players? Are there any specific aspects of the game that you find particularly difficult, or does the overall experience simply require a higher level of skill and strategy than other games in its genre? I'm curious to understand the challenges that Sekiro presents and what sets it apart from other similar titles.