It is a profoundly erroenous truism, repeated by all copy-books and by eminent people making speeches, that we should cultivate the habit of thinking of what we are doing. The precise opposite is the case. Civilization advances by extending the number of operations which we can perform without thinking about them. Operations of thought are like cavalry charges in a battle--they are strictly limited in number, they require fresh horses, and must only be made at decisive moments.Making decisions is energy-consuming. Subjects who use their willpower to eat healthy radishes instead of the available and sumptuous chocolates are less likely to persist in solving unsolvable puzzles. Subjects who are told to suppress emotional reactions to a movie are less able to solve solvable anagrams.
We have a limited amount of decision-making power to allocate on a moment to moment basis. That is why developing small but healthy habits that over time will become automatic is so money.