Then he is very sure. 
( Then ( he ( ( is ( very sure ) ) . ) ) )
(ROOT (S (RB Then) (NP (PRP he)) (VP (VBZ is) (ADJP (RB very) (JJ sure))) (. .)))
He is very sure of himself.
( He ( ( is ( very ( sure ( of himself ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBZ is) (ADJP (RB very) (JJ sure) (PP (IN of) (NP (PRP himself))))) (. .)))