Stress is a big problem in exam situations

Of course, too much stress can be an issue, but you do need some stress to help you perform.

You should revise till you drop before an exam

You shouldn’t even look at revising on the day of the exam

Neither of these are true.  Get a good night’s sleep, don’t be up until 3 revising, but a quick scan of your summary notes on the day itself can help to reassure you you’ve done all you can, if nothing else.

Planning exam answers is a waste of valuable time

This is the most destructive exam myth.  Even when you don’t have much time per question, planning will help you to use that time better, not waste it.  If you were to run out of time and not finish, the examiner can see where you were going from your plan, and you can be credited for points you clearly show in your plan.