He won the majority because he was vastly superior to any other player (bar Rafa on clay). He doesn't have a great record in tight - especially 5 set - matches.
Then again he has a great TB record which shows mental strength, of course.
His BP convertion was atrocious too on ocassions.
He won because of how superior he was to the rest of the field. His mental strength wasn't something outstanding like Sampras's or Nadal's