dreamer, you need to get the basics down pat. If you learn the book knowledge well & don't have to think about that it gives you more time to solve problems. Wasting 10 seconds here & 10 seconds there repeatedly because you don't know the basics well enough soon adds up.
Separation standards, local instructions, frequencies of surrounding units, coordination requirements, using the HMI (human machine interface).
I'm not so sure it's nerves that does most trainees in. Sure, nerves & stress are considerations but you still have to be able to pull the entire package together & perform to the required level. Some people just can't pull it all together sufficiently well.
In the end if you ain't got it you ain't got it. And then you have to do it all again for real.