2. External cause. For example, upon seeing your neighbor with a nice car, a thought comes up: I must buy a car better than that one. The thought wouldn’t have come up if you did not see the neighbor’s car in the first place. So, seeing the neighbor’s car is the external cause for this desire to arise.

~ Depicted from "THE HANDBOOK FOR LIFE"S JOURNEY : On The Three Poisons - How to Handle Desire"