The first principle is that economics is fundamentally about reward for effort. The use of the word economical reflects this. An economical car will go further on less fuel. An economical furnace will produce more heat while consuming less power. Nature is also economical; water and electricity will take the path of least resistance. So it is with humans. Given a choice, humans will choose the option that gives them the most reward for the least effort. For example, all other things being equal, we will go to the nearest store to make a purchase. When applying this principle it is important to remember that we are dealing with humans, and that some habits can take a lot of effort to change.