Buddha once said: "Imagine all the billions of universes/galaxies were equivalent to a vast ocean and there was a bucket floating on its surface. Consider that a blind turtle lived in the depths of this huge ocean. Once every 100 years the turtle would come to the surface to breath and then return to the bottom of the ocean. The probability of that old blind turtle to hit its head on the bucket once surfacing to breath is as rare as the chance of obtaining a human birth."
 
The moral of the story is we should never take our human birth for granted. Instead we should be grateful and reflect on our immense good fortune and use this lifetime wisely to purify our mind/heart and thrive to become better human beings.