There's no guarantee that even an experienced controller wouldn't "lose it" one day if disaster strikes, although it's probably unlikely.
But the ability to hold it all together in an emergency is not necessarily the characteristic that determines if one is going to be able to do the job or not. The job itself is fairly unique and provides all the testing required to provide that determination. Responding to emergencies is a very small part of that job.
Emergencies are something trained for and practiced that we think about and pretty much hope never happen.
Minor to significant emergency situations are not uncommon, over a lifetime, however I expect to go through my career without seeing a major crash.