Just read The Wealth of Nations by Adam Smith
actually, don't even read it, just listen to what was consider his most notable concept.
The "Invisible Hand" is the idea that people do things in there self-interest.
Now before you say anything about morality, just remember, morals are relative, and people donate things to the needy because it makes them feel good, its basically a drug(really, its a hormone)
Lets imply self interest to paying for your grocerys
You pick the shortest line because its faster, but everybody else wants a short line too, so all the people look for shorter lines. This will eventually create equilibriums.
Now replace lines with investments