Sacrifices are typically called for when values conflict—two valuable things cannot both be had and one must be given up for the sake of the other. But not all sacrifices are self-sacrifices. For instance, the person who gives up something that benefits their self for some greater benefit to their own self—leaving the comfort of a spacious house in order to live in a small apartment closer to work—makes a sacrifice but not a self-sacrifice.
For something to count as a case of self-sacrifice:
There is some intentional ambiguity in this definition, because ‘constitute,’ ‘benefit,’ and ‘matter to’ are three different possibilities. Something can be said to constitute someone if it is their self or is part of what is their self. A sacrifice is of something that constitutes the self if someone sacrifices their life, or, for instance, their memory, their limbs or organs, their dignity, their identity, their integrity, or their basic capacities. Something benefits someone if it is something that is in their narrowly understood self interest to have or keep. For instance, someone who gives up an opportunity for a job interview, or their resources, or their physical comfort, is ordinarily understood to be sacrificing something beneficial to them as an individual. Something matters to someone if it is something that is important to them, something that they care about, that they value, or love, or are committed to. If people can have an obligation to make a certain self-sacrifice, they might be obligated to sacrifice something that matters to them; they might even be obligated to sacrifice that which is more important to them than anything else.
For instance, parents who affirm their adult child’s decision to participate in a dangerous, even life-threatening, humanitarian intervention are willing to sacrifice their child, whom they love more than anything, for the sake of the worthy goals of the intervention. The person who chooses to participate in this sort of dangerous action clearly makes a self-sacrifice (of their own safety and perhaps their life), but so do those who love them, by virtue of sacrificing what matters to them the most, and doing so for the sake of someone or something else.
What constitutes the self, or what benefits the self, might also matter to the self, or might not. And what matters to the self might also constitute or benefit the self, or might not. Even if what constitutes or benefits the self matters to the self, someone or something else might matter more.
If we were psychological egoists, then only our own selves (or our well-being, and so on) would matter non-instrumentally to us; everything that we valued would either (partly) constitute or benefit ourselves. However, we (that is, most of us) are not psychological egoists; we typically value in both egoistic and altruistic ways, as well as impartially. That’s why something that neither constitutes nor benefits us in a narrowly self-interested way may still matter to us. When we value something (or someone) more than we value our own self, and when forced to choose between what constitutes or benefits our self, and what matters the most to us, we may protect what matters the most to us rather than our own self. This will seem obvious to every parent who works themselves to exhaustion so their child can have a better life, or who knows that they would readily die for their child. When it is clear that what matters the most to us is what really matters the most—that what we most value is what is most valuable—it is also clear that sacrificing for the sake of what matters the most to us is warranted, though it may still be tragic.
Cases of self-sacrifice are complicated because a person may not value their own self, or something else that matters to them, in the way that in some sense they ought to. They might overvalue or undervalue their own self; or, whatever (or whoever) else matters to them the most might not be what (or who) really matters the most. This may lead to their self-sacrificing when they ought not, or failing to self-sacrifice when they ought to.
We shouldn’t take for granted that what matters the most to us is what really matters the most. When something goes wrong in the process of forming our values, we should be suspicious of whatever values we end up with. Women who have been socialized by coercive gender norms to be particularly self-sacrificing might not value their individual selves enough, because something has gone wrong in how their values were shaped. “Do-gooders” might have a similarly self-sacrificing system of values, not (necessarily) due to coercive gender norms, but due to a kind of pathological altruism. But there are others who err in the opposite direction: not self-sacrificing enough, for instance, by acting to unfairly advantage their own families while not working politically to make the mechanisms of opportunity hoarding unavailable. In this last case, perhaps anxiety about whether those they love would fare well enough under more egalitarian norms taints how values are formed.
There is no easy answer to the question of what matters the most, especially when there is conflict between two things that really do matter. But to know whether we are self-sacrificing too much, or not enough, we need to at least open the question.