Any experienced adult is aware that we make many (cynics would say all) of our decisions on the basis of our self-interest. After all, if we completely ignored or sought to destroy our own well-being, we wouldn't still be around. Still, some actions don't seem motivated by profit--a mother's sacrifice of her life for her child's safety, for example (though a sociobiologist might argue that preserving one's genetic structure through one's offspring is in one's self-interest). Certainly, only the most cynical observer would argue that Mother Theresa was motivated by greed.
Unfortunately, more common than acts of unselfishness are actions that risk safety or cause harm with no apparent benefit to anyone (drunk driving, for example). Although acts of love or sacrifice may seem to contradict the notion that people are motivated primarily by self interest, self-destructive acts truly undermine the notion that people seek first to benefit themselves. If we really wanted to maximize our lifespan, why would we smoke (or overeat, or drink to excess, or drive on I-285, or whatever)? Some might argue that we prefer an interesting, dangerous life to a boring safe existence (as in the Sylvester Stallone classic Demolition Man), but it's hard to believe that the coughing, retching wino in a cardboard box under a bridge is really acting in his own self-interest.
We often use the adjective "rational" or "reasonable" to describe actions that promote our well-being, and the adjective "irrational" or "unreasonable" to describe actions that threaten or harm us. Often (and certainly in much Greek literature and philosophy) the irrational is characterized as excessive, while the rational is described as moderate. It's reasonable to have a beer with your enchilada dinner; it's unreasonable to drink six margaritas in an hour. "Nothing to excess" is written over a Greek oracle. "Wisdom, Justice, Moderation" is the Georgia motto.
Unfortunately the owner's manual we were born with doesn't spell out where moderation stops and excess starts. It's irrational (crazy) to spend all of your monthly paycheck on lottery tickets, but certainly buying one lottery ticket isn't excessive. Or two tickets. Or three tickets . . . . What about a person with deep-held religious beliefs? Does standing up for those beliefs make her a weirdo? The answer usually depends on the person answering the question.
Even if we all agree that a certain action is irrational, we can be sure that someone, somewhere is committing that action. So we're left with the question, "Why do otherwise sane people do crazy things?" In the wake of recent school shootings, reporters and "experts" often chose the easy answer: that the shooters were in some way crazy, driven to their extremes by videogames, violence on television, Marilyn Manson lyrics, or whatever. These experts seemed unable to come up with a rational explanation, and furthermore denied the choice the shooters made in playing the videogame or buying the Marilyn Manson CD. Maybe the answer is that there is no rational justification for an irrational act (which is just another way to avoid answering the question).
If you were in a store and and knew you could steal a CD without anyone seeing you, would you do so? Why or why not?
If you knew of a broken pay phone that let you make free long-distance calls, would you do so?