From Ecce Homo:

In all these matters — in the choice of nutrition, of place and climate, of recreation — an instinct of self-preservation issues its commandments, and it gains its most unambiguous expression as an instinct of self-defense. Not to see many things, not to hear many things, not to permit many things to come close — first imperative of prudence, first proof that one is no mere accident but a necessity. The usual word for this instinct of self-defense is taste. It commands us not only to say No when Yes would be “selfless” but also to say No as rarely as possible. To detach oneself, to separate oneself from anything that would make it necessary to keep saying No. The reason in this is that when defensive expenditures, be they ever so small, become the rule and a habit, they entail an extraordinary and entirely superfluous impoverishment. Our great expenses are composed of the most frequent small ones. Warding off, not letting things come close, involves an expenditure — let nobody deceive himself about it this — energy wasted on negative ends. Merely through the constant need to ward off, one can become weak enough to be unable to defend oneself any longer.