All For One

There's basically various ratios at which someone else can trade their wellbeing for you own.

There are people who seemingly care ~0 about your wellbeing, only their own; they would happily steal your $1000 suit to use as a floor rag, because the 0.1 units of value they get from that is worth more to them than the 1000 units of value you lose by losing it.

There are other people who are too self-sacrificing: you ask if they have a kleenex and they give you their silk tie. I'm not sure why but this is also very bothersome, to me at least.

I'm totally speculating here but maybe the common amount is for people to care about themselves about ~2x as much as the people around them. These are the people who will cut ahead of you in line (or something) – the benefit they get from that is 1:1 with the benefit lost by everyone else combined – but they wouldn't steal your sentimental watch.

I suspect the most charming conversion rate that someone can use is roughly one-to-one: they basically consider your well-being as much as they consider their own, but not more. I'm not sure that's true, but intuitively it feels true.