I used this analogy today with a customer who had complaints of how "cold" the air was coming out of his registers. I will spare you on all the details and I'll share this, house temp maintaining 68 degrees, with outlet air temp of 73 degrees. A major contributing factor to this was where the return air was coming from, which was an unfinished, uninsulated, and un-tempered walk-out basement. Basically a large heat-sink. 

The second law in thermodynamics is "heat seeks cold" or heat moves from hot to cold. Transferring btu's is all we are doing. He went on to emphatically say that his register air should be warmer. Which I agree with, however, the heat that he was expecting, was also being robbed or absorbed by the cold. 

So I used the "Cooler" analogy, and asked him to think in reverse, to help him understand a bit better. Suppose you get a bag of ice from the gas station, and you put the ice in a cardboard box, how long will it last? Now put that ice in a insulated cooler, how long will it last? The "heat" will seek the cold and eventually melt the ice, but the amount of work or time it will take is impacted by the "insulation" of the container. Keeping a container warm works the exact same way.  

Infiltration plays a major role in our industry, weather it be heating or cooling season. Every piece of equipment is, and can be impacted by this, and performance will suffer. It does not matter how big the piece of equipment is, or the technology on how it works, nor the efficiency rating for that matter. If the space itself is not properly constructed, and equipment is not installed properly, it will never "feel" right.