When I was a child, I wanted to be like Spock. For those few who do not know whom I mean, Spock was the science officer on the star ship Enterprise in the famous 1960's sci-fi television show Star Trek. His claim to fame was being half-human and half-Vulcan. Vulcans were an alien race who are so naturally violent that they felt themselves forced to renounce their emotions and turn to a life of pure logic, lest they extinguish themselves in endless war. A common misconception is that Vulcans have no emotions; they do, but they rigidly suppress them.
Spock's major character arc involved a conflict between his "human side" and his "Vulcan side", between "emotions" and "logic". During the television series, he had chosen to attempt being pure Vulcan/logical, but he met with less success than he would have liked. Something never made clear was whether this was purely a personal issue or if perhaps being only half-Vulcan made it somehow biologically more difficult to live with the Vulcan philosophies and disciplines. (Most likely even the writers themselves were conflicted over their interpretation of this.)
Spock's initial choice reflects a common view of emotions, that they are intrinsically opposed to logic, unpredictable and uncontrollable, that you are forced to choose either the cold, cruel world of logic, or the squishy, utterly irrational world of emotion and feeling, but that ne'er the twain shall meet. This is view can be seen in our most ancient literature, where the fiery passions of somebody's loins are routinely contrasted with their cold, austere logical mind.
What absolute garbage!
It is not true that logic is a cold, cruel discipline. Logic is nothing at all; it is merely a way of manipulating a set of statements with some truth value to obtain new statements with some truth value. What is cold and cruel is not logic itself, but the axioms fed to the logic system to get it started. Certainly if you start with axioms like the axiom scheme for universal instantiation, then you are going to end up with a logic that is not capable of dealing with emotion. But then, it's not capable of dealing with much of anything outside of pure math without fully specifying the universe, something generally considered impractical. (And possibly not even if you did provide such a specification; it is impossible to prove that the Universe works solely according to any given logical axiom system.)
On the other hand, feed logic what you know about emotions from life, like
If you prick us, do we not bleed? if you tickle us, do we not laugh? if you poison us, do we not die? and if you wrong us, shall we not revenge?
and use a form of probabilistic, experience-fed logic we call "common sense", and by golly, those emotions become highly tractable and reasonably predictable.
It is true that mere knowledge about emotions does not intrinsically allow you to manipulate them; the mere knowledge that you will be angry does not prevent you from becoming angry. However, it does allow you to indirectly manipulate your emotions, or the emotions of others, by giving you the insight to prevent the anger-inducing situation from arising in the first place, or if nothing else at least allowing you to prepare yourself for the anger and perhaps mentally rehearse your actions before your emotions determine them for you.
There are a lot of people who try to deal with their emotions as Spock did, by rigidly suppression or denial, and as a result, they assign no value to their emotional well-being, assuming it to be something they can simply ignore or change with raw willpower. But there is a value to your emotional well-being, a value greater than zero, and this should never be ignored or downplayed because of stupid ideas about emotions. You should not consider the value of loved one's emotional well-being to be zero either; this can be harder since you don't directly experience their emotions.
This concept will generally not come up directly throughout this book, but it is a constant background presence. Your mental state is always a consideration in programming decisions. On the trivial level, the answer to the tricky problem of weighing the costs and benefits of five competing solutions to your problem may be to give up for the night, call a couple of your friends, and hit the bar for the rest of the night. This is not a joke.
On a more serious level, if you are constantly being forced into sub-optimal solutions by an authority figure and the prospect of having to spend another month patching servers and restoring backups that could have been prevented if you had just been given the opportunity to take two days and write the input parsing routines correctly, when it comes time to decide whether or not to keep the job or look elsewhere, do not make the mistake of valuing your emotional state at zero. Only you can decide the exact value, but you should make that decision with the full awareness of the value of your emotions.
If you are making programming decisions that affect a team, you mustn't ignore these factors either. Working your team 80 hours a week isn't a neutral decision, because not only are they not really doing 80 hours of work anyhow (one of the few facts about productivity that has abundant scientific support), but you are wrecking their lives, burning them out, and, if you still can't find it in yourself to care about that, greatly increasing the chances that you will lose employees, which also represents a loss of knowledge and skills that can only be painfully replaced, if that.
Programming seems to attract a lot of people, both managers and managees, that somehow have come to the conclusion that being human is a failing that can be overcome merely with sufficient will power. Pervasive belief does not make it true.
You are not a Vulcan. You should not plan to live like one.