Please help me follow this explanation.
"We use the preposition "de" after the adjective..." by adjective do you mean facil/dificil?
when the subject is "the thing" (el armario) - Can you expand please as to what "the subject being the thing" means? What thing? What does thing refer to here?
"...not when the subject is "doing something" (montar el armario)." Isn't the subject always doing something? I don't understand this distinction.
All the examples are great and I can sense the pattern but I'd like something more concrete to be able to lock-in to the rule please :-)