One of the hardest things to do is see the impermanence of things. It’s a lesson most people learn relatively early, like when a pet or relative dies, or they go through a bad breakup. Those situations are most painful when the presence of something good in life had become so deeply ingrained that not having the good thing was unthinkable.
So, when you lose it, you go through a not-insignificant amount of suffering that can range from a few days of feeling a bit numb to months of dully staring at everyone around you, wondering how anybody manages to go through their daily routines when there’s so much suffering to be had.