Sentence:  We speculate that compulsives in the unstructured schools are under greater strain because of the <WSD>lack</WSD> of systemization in their school setting , but that their need to organize ( for comfort ) is so intense that they struggle to induce the phonic rules and achieve in spite of the lack of direction from the environment . 
Meaning of the word marked with <WSD> tags:  the state of needing something that is absent or unavailable