In Hamlet, what lesson does Hamlet tell Horatio he has leared about life and how does that lesson show a change in Hamlet's character?

Hamlet has spent the entire play
thinking about what do and thinking  about how
to do it, and thinking philosophically about why people don't do
things.  The thing he realizes by the end of the play is that all this thinking isn't
accomplishing anything and that he finally just has to ACT and REACT to whatever comes
his way. 

At the of Act 5 is has decided to go into the
fencing match with Laertes.  Horatio has warned him that this could be dangerous, but
Hamlet responds by saying, "We defy augury; there's a special providence int he fall of
sparrow.  If it be now, 'tis not to come; if it be not to come, it will be now; if it he
not now, yet it will come: the readiness is all."  This is a refreshing attitude for
Hamlet.  He is essentially saying that while God knows about even the smallest events in
the universe, we don't, and all we can do is be ready for whatever comes our way. 
Hamlet is giving himself over to fate rather than cursing it or trying to control it. 
This new understanding of fate frees him to act.  He faces the unknown and accepts that
what will be, will be.