Fat is the new Carb!
I explained it to my Fit For the King folks kinda like this. You are wanting to start a bon fire. Your choices for fire in the firepit are Oak logs (Carbs), Pine Logs (Fats) and Coal (Protein). The oak is the natural first choice, it burn clean, burns long and lights fairly easily. The pine is not your first choice but will work if there is no oak. It burns fast, smokes a lot and needs to be replaced more. The coal will burn, but takes more energy to start and to keep burning. It produces great heat, but is harder to keep going. We would prefer to use the oak, but will use the pine if we have to, it just takes more work. Our body prefers to use carbs for energy but will use fat if carbs are not available. Fats are not as efficient, but they can and do get the job done. If neither are available, the body will use proteins, taking them from the hopper, thus reducing the reserve.
A stupid illustration, but it helped my folks understand a little more clearly how the body uses the macros.