Good lord people, its a suggestion of "3"s then.
Obviously if you are lost in the desert you may put Water before shelter. Just as if you were stuck above the tree line in a Blizzard then you would put shelter before water, it's common sence. The senerio is going to dictate what the most important surival factor is!
If an armed intruder comes into my home, I don't need to go get my tent, or my camel back, I need to reach into the night stand and pull out my .357 mag.