Why does Hamlet find it so difficult to carry out his promise to his father's spirit? Why does he not act immediately?

Hamlet is a thinker. He wants to know the ghost is an "honest ghost" rather than the Devil who can "assume a pleasing shape". Hamlet must contemplate the nature of life, revenge, and the afterlife before he can carry out his revenge. Many believe that Hamlet's inability to make impulsive decisions is is tragic flaw.