This advice comes up very often when people write about re-evaluating their lives. (Also, this retort comes up very often when people read what those people wrote. I don't disagree with your logic, per se...)
I think you're right, but the author probably did not mean the advice as literally as you're reading it. You're interpreting the advice as a call for egoism [0]; selfishness to the point of being unwise. I think that when people write this, they're actually writing a call for hedonism[1].
Hedonism is different from egoism. Hedonism, the way I see it, is realizing that our existence is ultimately meaningless, and that we should optimize for our own happiness (and well-being) rather than any other metric; all metrics are meaningless, so we might as well stick to what makes us happy. In actionable terms, embracing hedonism means realizing that you should aim towards doing things that make you happy, and that this aim should be your guiding force (at every "single moment in life"). This doesn't mean that you should be happy every single moment; it means you should be optimizing for happiness every single moment. (To use your examples: a spouse knows that compromising will make them happier overall; a janitor knows that although his/her life aren't perfect, doing this is what will lead to his/her life improving (hopefully) or at least keeping them happier.)
Anyway, that's the way I understand this type of advice, and I appreciate the occasional reminders. (Also, I don't actually know much about philosophy, so I might be misusing terminology here; if so, please correct me!)
Yes, read flatly this advice is borderline egoism, but it can be read in a more useful way if some ideas are added.
You shall not want to do something that you would not want others to be allowed to do. (Eg: you cannot want to kill people for fun in the streets. That's a Kantian principle, IIRC)
You should better have a long-term perspective on what you want to do, and why. If you are tooth ache, your primary self probably do not "want" to go to dentist, but your reasonable self tells you that you have to do it, even without any immediate wishes to go.
Even if you were Xi Jinping or Obama, you cannot control everything you wish to control. The stoistic advice works here: you should do all you can to prepare yourself a nice cruise (or life), but once on the boat, you can't help if you are caught in a storm and should better shut up than complain.
An example is marriage+kids: you should probably jump carefully on this little boat, but once in, better eat your hat than jump overboard at the first annoyance.
I think you're right, but the author probably did not mean the advice as literally as you're reading it. You're interpreting the advice as a call for egoism [0]; selfishness to the point of being unwise. I think that when people write this, they're actually writing a call for hedonism[1].
Hedonism is different from egoism. Hedonism, the way I see it, is realizing that our existence is ultimately meaningless, and that we should optimize for our own happiness (and well-being) rather than any other metric; all metrics are meaningless, so we might as well stick to what makes us happy. In actionable terms, embracing hedonism means realizing that you should aim towards doing things that make you happy, and that this aim should be your guiding force (at every "single moment in life"). This doesn't mean that you should be happy every single moment; it means you should be optimizing for happiness every single moment. (To use your examples: a spouse knows that compromising will make them happier overall; a janitor knows that although his/her life aren't perfect, doing this is what will lead to his/her life improving (hopefully) or at least keeping them happier.)
Anyway, that's the way I understand this type of advice, and I appreciate the occasional reminders. (Also, I don't actually know much about philosophy, so I might be misusing terminology here; if so, please correct me!)
[0] http://en.wikipedia.org/wiki/Ethical_egoism (maybe?)
[1] http://en.wikipedia.org/wiki/Hedonism