Explanation building is the inverse  starting with the observations, the evaluator develops a picture of what is happening and why.
( ( ( Explanation building ) ( is ( ( the inverse ) ( starting ( with ( the observations ) ) ) ) ) ) ( , ( ( the evaluator ) ( ( develops ( ( ( ( ( a picture ) ( of what ) ) ( is happening ) ) and ) why ) ) . ) ) ) )
(ROOT (S (S (NP (NN Explanation) (NN building)) (VP (VBZ is) (NP (NP (DT the) (NN inverse)) (VP (VBG starting) (PP (IN with) (NP (DT the) (NNS observations))))))) (, ,) (NP (DT the) (NN evaluator)) (VP (VBZ develops) (SBAR (SBAR (WHNP (NP (DT a) (NN picture)) (WHPP (IN of) (WHNP (WP what)))) (S (VP (VBZ is) (VP (VBG happening))))) (CC and) (SBAR (WHADVP (WRB why))))) (. .)))
Observations are the last part of explanation building.
( Observations ( ( are ( ( the ( last part ) ) ( of ( explanation building ) ) ) ) . ) )
(ROOT (S (NP (NNS Observations)) (VP (VBP are) (NP (NP (DT the) (JJ last) (NN part)) (PP (IN of) (NP (NN explanation) (NN building))))) (. .)))