Rational self interest is taking into account negative consequences for solutions to a problem at hand and acting to achieve the best result for yourself. EG Im hungry, I can eat the largest ears of corn now, which will select for smaller ears in successive generations or I can eat the smallest ears saving the large ones for planting so as to select for production increasing yields and better dealing with successive hunger.
Life is one continuous self indulgence, I piss when I need to, eat when necessary. Smoke when I get the urge. Sleep when my body needs it. Work to pay for what I need. Copulate to feel good and produce progeny. etc etc etc. You wouldn't do something if you didnt have a compelling reason. eg I give to charity because it makes me feel good about myself and reassures me that I am good person. I listen to a friends complaining because I want to maintain the friendship, what I am listening to is a minor inconveiniance as I know my friend wont always complain and we will eventually do something fun. People lie to themselves all the time about their motives, especially with examples like I CARE ABOUT THEM, or I give cuz I care about the poor. Lets face it, it makes us feel good. Greed can have rational limitations as well. If I want to keep all of the goods to a kingdom to myself and kill all my subjects i have to do all the labor myself... not very kingly. Thats why they allow us serfs a modicum of standard of living. Because they have to to keep control.