As you sow, so shall you reap. What goes around comes around. What you give is what you get.
Can you recall a moment when you were standing at the edge of a cliff and called out in the distance. You heard an echo from far away coming back to you. Or even an empty hall where any sound you made would rebound on the walls and ceilings. Just a few months ago, I heard a dog barking relentlessly in our neighborhood. Instead of just a single bark, one could hear the exact same bark echoing twice into the distance. It seemed as if the dog was barking at himself/herself. This is how it feels at times when the energy you put out into the world seems to come back to you two-fold or three-fold in magnitude. Call it a boomerang. Or call it Karma.