what do you mean by "fucked in the head"?

I think there are times where, even if you are capable, it's best not to do something if the psychological strain would be too intense, it can easily trigger more serious mental health issues that become harder to escape once your livelihood depends on it.

I once considered being a neurosurgeon & decided to interview a well known guy in the field. he told me that if I want a life & family then this is not the job for me. the intense work, long hours, weekends, always on call, he never sees his kids & his wife left him & he doesn't blame her.