Yes huge amount of luck. I think there is more luck that many would like to admit in professional football (or sport). To some extent you make your own luck of course but our lack of injuries, limited suspensions and the fact that several of our players seem to have reached that sweet spot in their career at the same point have contributed.
Ranieri is an extremely experienced manager, the fact that he has had to make limited changes to a team which was on a tremendous run before he arrived has been important.
The tactics have changed subtly throughout the season, Vardy was the force that won us some many games early on. Then the defence took over, we've gone 1-0 up in some many games recently it makes it very difficult for teams to come back at us without conceding more.