> I do tend to assume that people will act in what they believe to be their own self-interest. (With some emphasis on "what they believe to be".)
I think that's a useful assumption for economics, but not realistic. How does it explain soldiers, risking their lives and health for low pay and horrendous working conditions? People working on free open source projects? People spending extra money on social benefits, such as fair trade coffee or electric/hybrid cars (that is, electric cars that aren't status symbols)? Political activists who dedicate their lives to a cause? People choosing to be parents?
Many people who join the military do it because they have few better career options, and the probability of death or serious injury still isn't extremely high. So in that case it's driven by economic self interest.
Self interest can also mean pursuing non economic benefits that nonetheless provide real, though harder to quantify, value. Like joining the military to gain the respect of your family or community.
Similar motivations around open source code contributions.
People buy fair trade products due to guilt, and I don't say that as a criticism - guilt can be a very pro-social emotion.
Political activists are often motivated by a desire to be accepted and held up by a belief community, whether religious or secular.
And being a biological parent is among the most self interested things you can do.
There are definitely selfish reasons to do all of those things. Examples:
> How does it explain soldiers, risking their lives and health for low pay and horrendous working conditions?
Soldiers defend their own families and friends against invaders who would kill or enslave everyone. That's perfectly reasonable, but it can also be considered selfish.
> People working on free open source projects
FOSS projects can be very interesting and rewarding work, not monetarily but in other ways (in excitement, reputation or maybe glory).
> People spending extra money on social benefits, such as fair trade coffee or electric/hybrid cars
Electric cars are better for the environment, and I imagine many people want a clean environment for everyone, themselves included.
> People choosing to be parents?
One reason to have kids is to have someone to take care of you in your old age (both materially and emotionally). Many people hate the idea of growing old alone.
That wasn't the point. The discussion was about self-interest, not rationality. People act out of self-interest all the time, even when appearing altruistic (it just happens that sometimes the interests of others align with your own interests).
I think that's a useful assumption for economics, but not realistic. How does it explain soldiers, risking their lives and health for low pay and horrendous working conditions? People working on free open source projects? People spending extra money on social benefits, such as fair trade coffee or electric/hybrid cars (that is, electric cars that aren't status symbols)? Political activists who dedicate their lives to a cause? People choosing to be parents?