A man is murdered, his wife benefits from his death, as his will entitles her to his estate worth $100 mil in its entirety. Police rightly suspects her as the murderer – because she has the most incentives to do so: $100 mil.
That’s rational thought.
This is irrational thought:
A man is murdered, his wife benefits from his death, as his will entitles her to his estate worth $100 mil in its entirety. Police suspects a common street guy who just happened to pass by when the murder was committed.
That is to say, of course, that evidence points nowhere. But sometimes evidence can point both ways – to the wife, and to the streetwalker. And that’s all the evidence you can find. No CSI team can find other evidence.
Assuming, of course, that everyone doesn’t lie (except the murderer) and everything is ideal (such as the murdered man is the perfect gentleman, doesn’t smoke or drink, in perfect health etc.), the best thing an investigator can do is to look for the incentives. The wife would rank up very high with incentives, while the streetwalker ranks at the bottom.
Of course, the wife’s benefits would also be a positive externality – a by product of the husband’s murder (assumed to be killed by the streetwalker). Or, the streetwalker’s arrest could also be a negative externality – a by product of the man’s murder (assumed to be killed by the wife); that would mean that the street walker was extremely dumb.
Hmm.. think about it. Which one are you? The rational one, or the irrational one?
Come to think about it… I’ve been in a lot of irrational situations before, where people start accusing the people with the least incentive, because conventional wisdom says so. Well.. we can’t all expect everyone to act rationally, can we?
Dude, your irrationality is not irrational enough. To be truly irrational, one should assume that it was a highly skilful assasin who was hired to kill the man who actually was a boss of a high ranking organised crime gang.
The assasin then couldn’t care less about the wife since:
Of course, that’s making a story that is irrelevant to your post – but I believe in equal opportunity. There is always the funny story of the passerby actually being kinda insane. After all, we have the case of the wife being extremely clever and is trying to frame this passerby – or – that the passerby is a little insane and would get away with it (unless he/she happens to be an assasin).
Then we can also have the case of the really stupid wife. Come on – would you go leave evidence all over the place that you killed your husband?
If you were the first person to become suspect – you would already have thought of a way to clear your name or frame someone else, no? After all, women are supposed to be the smart ones. 
So speaks the actuarist
.
But the point is of course, to display a disparity between incentive and non incentive. A better story would be of course, to accuse someone who stands to lose all his life savings and assets if the man died.
Now, that’s truly irrational.
Society tends to guide everything towards ‘rationality’ as it prevents too much of the unknown and unpredictable. But who defines what is ‘rational’ and ‘irrational’?
Actually, society is… unpredictable. As for what is ‘rational’ and what is ‘irrational’, it’s a philosophical debate, but try this one on for size:
Riiight… I need to fix my blockquote. I thought I had used a transparent gif. Blur me
Stop being irrational and fix it. It wouldn’t take you more than ten to fifteen minutes. Your readers will appreciate it (well, if most of them don’t, I will).
I fixed it… comments?
i believe in a vague instance as this, there isn’t a ‘rational’ thought because both thoughts have no solid foundation/proof. They’re merely speculations based on personal logic (which differs from individual to individual). You cannot rationalize anything unless there is a degree of certainty or a definite sense that one choice is better than the other.
To me, although i also agree the first thought could seem more ‘rational’, as long as both thoughts are possible, there isn’t a right answer.
nice post!
More random rational-irrational illustrations:
If my blog’s link suddenly appears in Freakonomics’ or Tim Harford’s blogrolls without their knowledge, I’m suspect No.1
^This is rational thinking, since I have much to gain, it would be an incentive for me to force my way into their blogrolls.
If my blog link suddenly appears in some spam sites, and I’m suspect No.1 for doing that
^This, is irrational thinking, since I have much to lose, and it would be an incentive for me to stay away from spam sites, what more add my link to spam sites.
Maybe it wasn’t his wife nor the street guy? What if human beings are really evolving and someone has mastered the power of invisibility (I’ve got to stop watching ‘Heroes’)?
Lol.. that’s totally outta the box. No more confined within the box of rational-irrational. Just probabilities. Because there is always a probability that someone turns invisible.
Just out of hilarity – what about if you killed that man?
Shouldn’t you be the one calculating the probabilities of that happening?
Besides, I should act like a spectre, or some invisible, ethereal being… you know… Observer of All Mankind and Holder of All Time… that sort of thing.
Been there, done that – trust me, it’s not as fun as you think.
To each his own… I find observing more interesting than actually participating XD
Matter of money always seems quite string in these things. But of course the police sometimes forgets to consider another reason.