Suppose you trained for many years to be a cook of some kind.
It occurs to you that this expertise you have, rather than merely earning money, or rather than merely gratifying humanity's instinctual urges, could somehow make the world a better place.
Skipping over the vagaries of volunteerism that ensue, a series of seemingly well-intentioned and self-sacrificing decisions results in your being appointed to the position of head chef at a special hospital for the severely mentally disabled.
At first you undertake your work with a sort of default attitude of doing the best you can. Soon enough, however, it is clear that this is not entirely pleasing to the inmates: they do not share your sophisticated sense of taste, and it is not entirely clear to you if they had become accustomed to being force fed baby food under the prior regime or what exactly. You have brought with you a notion of cuisine quite incompatible with the expectations of your captives, who can only express their relative pleasure or displeasure with inchoate and stochastic noises.
Inevitably, of course, there are also ethical considerations: they have not chosen to be vegan, but you may be vegan on their behalf, so to speak, and they cannot articulate their dissatisfaction with this decision of yours --nor can any sense be made out of what dissatisfies them with the food from one day to the next.
With the passage of time, however, the most demoralizing aspect of the situation is this: as a volunteer you are paid nothing, but moreover you can never earn any kind of positive response from your small audience. If you were an unpaid employee at a normal restaurant there would at least be the possibility of seeing a review posted by a customer on the internet, or hearing from one new guest that they'd been recommended to try the place by another, and so on. There might be some friendship between you and a few of your regular customers, or some esprit de corps amongst you and your colleagues within the kitchen. All of that is absent from your lonely post as the volunteer chef at this particular asylum.
The significance of your best effort, in this context, feeding captives, unpaid, is increasingly unclear: would you be better off making the least effort possible, and conserving your energies (or even your money) for some other venture, given that there can neither be a tangible nor an intangible reward for doing the best you can at this one? Given that you can never even make your audience less miserable, why make yourself miserable in the act of catering to their desires?