exam fever

exams are something everyone had to go through in their life atleast once. Its mandatory that atleast one exam everyone would have written. It is common sense that u become experienced in something which you do regulary and it becomes ur habit. But most people find exams to be difficult even when in their life they have given 100 or more exams in total. i was just wondering why is that so? why do people continue to be scared of exams even when they reach M.phil or Ph.d or Post-doc?? it is not a primitiive fear response. it is definitely conditioned but the strength of the learning is so high that people cant get out of fear of examination. almost 99% of students wil study atleast the day b4 exams. otherwise they cant go on. anyway, it also has a survival value i guess, in the modern world...