lack of a pyschological center knocks it flat 
(ROOT (S (NP (NP (NN lack)) (PP (IN of) (NP (DT a) (JJ pyschological) (NN center)))) (VP (VBZ knocks) (NP (PRP it)) (S (ADJP (JJ flat))))))
(ROOT (S (NP (NP (NN )) (PP (IN ) (NP (DT ) (JJ ) (NN )))) (VP (VBZ ) (NP (PRP )) (S (ADJP (JJ ))))))