Here's how the game goes: one person lies on his back, while someone else starts tapping his forehead and tells him to name all the cereals he can in a certain amount of time.
What usually happens is, this person has trouble naming hardly any cereals. Same person who could probably rattle off a dozen of them with no problem, all of a sudden is stuck.
Because, quite, simply, things are different when there is pressure and resistance. Or someone tapping on your head.
How does one fix that?
Well, there's one key thing you can do that will go a long way toward alleviating this problem...
If you learn a system, and train hard to internalize that system so it is second nature, then you will hit it when it counts, under the lights and under pressure.