Which conflict in Hamlet is most mysterious in terms of its root cause?

This would be: why Hamlet does not seek his revenge on Polonius upon discovering Polonius's murdering of Claudius, Hamlet's father. It is unknown why Hamlet does not kill Polonius until he has been cut with a poisoned sWord and is already 'dead'. But it is essentially because he is too indecisive and pensive, when he should be impulsive and seek his immediate revenge.