The difficult chests are for a long time almost impossible to open in the game Kingdom Come Deliverance. For a much longer period than for the so-called very easy coffers, and those that are easy.
We must indeed wait a long time, the time to manage the doors and caches very easy and easy. Whenever you come across a possibility, exploit it to continually gain points and increase your picking level.
Difficult caches require a lockpicking level of 7.