Quotes about Lapsing

An interesting question these psychologists tend not to ask is why the muscle metaphor is apt. In other words, why is it that early successes at self-discipline lead to more successes, whereas early lapses lead to more lapses? If self-discipline is really good for the organism, you wouldn't expect natural selection to make it so easy for a few early lapses to destroy self-discipline. Yet there's no denying that a few injections of heroin can be the end of a productive life. Why?