Life, like this pile of rocks, is a puzzle - a free puzzle. Building a wall with these rocks (or any pile of rocks) could be compared to solving that puzzle.
To take a piece, and without inflicting huge changes with hammer or saw on it, place it in your wall where it actually seems to belong, is like taking life as it comes, and discovering a solution to part of the puzzle.
It may not be the only solution, but it is valid one. It is valid because you did it .
Nothing compares to that 'one-with-the-universe' moment, when you find a stone that fits so well that you just know it was supposed to be there.