After 8.4 million bodies, you get a human body. Just imagine, from bacteria, birds, animals, etc., 8.4 million lives later one gets a human life. In this human life, few get to know the real spiritual path. And among those, very few walk on the path and they are the lucky ones.
Adi Shankaracharya has also said that the human birth is very difficult to get.
So, a human birth, desire for a path, and the path being available to them (getting a Spiritual Master or Guru), these three things are rare and difficult to get. If you have all three, you are lucky.