The pictures and audio recordings, though, were more convincing. They seemed so full of life, so far from surrender: Why would any one of these people enter an airless meat truck in which they risked near certain suffocation?

On previous assignments in Libya, I interviewed migrants who tried to make it by sea. . Human smugglers carry them out from the beaches at night in small rafts to flimsy, overcrowded fishing boats. Some saw the dangers and begged to return to the shore, but the smugglers would not let them. Smugglers cannot allow witnesses to remain behind and, in Libya, they have forced migrants into the boats at gunpoint. Could smugglers in Serbia have used such force to cram the 71 people to the truck found in Austria?

Yet none of the migrants reported to their families that their smugglers carried guns. None recalled beatings or threats. Their recorded voices, until their last days, sounded unafraid, even confident. They had nearly reached their final destination.

I emailed my question — Why would anyone have freely entered the back of a meat truck? — to a social psychologist, Stephen D. Reicher of St. Andrews University, who is known for studies of the behavior of crowds under pressure. He sent back an exceptionally thoughtful response, which I will paste here (edited only slightly to correct typos):

The question you ask is fascinating, and, of course, the short answer is I don’t know. It is always hugely dangerous to try and explain phenomena when you don’t really know the details. It is a bit like asking a doctor to diagnose a patient they haven’t examined and where the symptoms are only hearsay. At the same time, the doctor could say something about the disease and how it works — leaving it open as to whether that applies in the specific case.

So I can say something in general about some (possibly) relevant processes.

Have you ever had that experience of going into a shop (for me, it is generally a bookshop) just to browse and without the intention of spending any money, then seeing three or four things that are interesting and feeling deeply conflicted about which two to buy — putting any back seems agonizing. Then you leave and realize that you were not particularly concerned about any of the books and quite happy not to have shelled out your hard-earned money on any of them. In other words, the nature of your choices and the value you put on any particular choice changes dramatically according to where you are.

So, in much more extreme form, when you are deciding whether to leave your country or not, the idea of going into a poorly ventilated truck might seem absurd. It threatens an extreme loss (of life) when you aren’t even convinced of the overall gain of leaving. But then you do make the choice to leave. You are near your destination. Now the choice is very different indeed. It is whether to fail, to have wasted all the efforts (and risks) involved so far or else to take a further risk and to (possibly) succeed.

In terms of Daniel Kahneman’s classic prospect theory of decision-making, the dilemma of the truck shifts from being taking a big risk to achieve a possible gain (getting to Europe) to taking a risk in order to avoid an otherwise certain loss (failing in one’s attempt to flee). And prospect theory tells us we are far more likely to take the latter risk.