Difficult is a synonym of Dense. Dense is the opposite of Simple. 
Should is related to Regret. Regret is related to Being. Being is related to Neat. Neat is related to Organize. 
Difficult <--Synonym--> Dense <--Antonym--> Simple 
Should <--RelatedTo--> Regret <--RelatedTo--> Being <--RelatedTo--> Neat <--RelatedTo--> Organize 