I don't think there's any link between exams and the real world, so stressing over exams doesn't necessarily say anything about how you'll cope with a job at all. It's a highly-focused period of a couple of hours which (even with resits) your studies up until then have focused on getting right "or else". My impression, from talking with my parents, is that the attitude towards exams has changed markedly since their childhood, where exams were obviously still important but also seemed to be rather incidental. One took them alongside one's education, rather than as a necessary result of it.
That's a change in attitude that is hardly the fault of the children, and it's hardly surprising that some are stressed out over life-defining high-intensity exams. I dare say it doesn't help that, no matter how well they do, it's difficult to escape the criticism that they're "easier than back in my day", thus belittling any achievements anyway.