What information do we learn about Fortinbras?

Young Fortinbras has arrived on Danish soil with an army of two thousand men. He plans to walk through Denmark to attack Poland. Hamlet is impressed that Young Fortinbras would risk so many men for a piece of worthless ground in Poland. Fortinbras lis a man of action who loves to fight. He becomes Hamlet's character foil. 

What does hamlet believe has kept him from acting decisively against Claudius