Worst-Case Scenarios vs. Occam's Razor

If you are friends with me on Facebook, you know that for the last six weeks I have been on my third-year pediatrics rotation. One of the key points that they focus on for babies' appointments (but that was not tested at all on our SHELF exam, which was frustrating - that's a rant for another time) is developmental milestones. 

Around the age of 12-18 months, most kids reach a point where they start to learn at least one new word every day, and they become nervous or even outright frightened at strangers. Around the same time, they may develop night terrors (in their deepest stages of sleep, that they usually don't remember, and often frighten parents or babysitters more than the the toddlers).

Around preschool/elementary school age, as most of you do remember, children start getting nightmares. They can't always tell what is real and what is not, and it manifests in sad and terrifying (and very memorable) images that haunt their REM sleep until they learn to remember what is real, and keep the bad dreams at bay.

Nowadays, as I learn a new skill or diagnosis or other piece of knowledge every day, it's again what I don't know that terrifies me. In my first two years of medical school, we learned the physiology of the human body and the pathophysiology of the many diseases that can ravage it. That was our equivalent of night terrors - terrifying information that we did not always fully grasp, and much of which is hazy in our minds after we are tested on it. And while medical student syndrome runs rampant ("Oh God, I totally have the symptoms I'm studying!"), I'm sure it is much more frightening or annoying to our parents, significant others, and non-medical friends - the ones who have to deal with us telling them about the latest disgusting disease manifestation we saw, or comfort us when we freak out about tests and grades and our careers. The ones who, when they asked us about their own medical issues, got the WebMD-style complete differential on the worst things that could be happening to them ("oh, your stomach hurts? Well, it's probably just gas, but maybe you're bleeding internally or you have a tumor or an intestinal blockage or... tell me more about your pain!").

Now, in third year, we struggle not only to relearn all of that information and then some, but to apply it to patients, and to retain it beyond just the next test. Because now we are in the second half of our training, and what we do now, more than anything before this, is going to shape our future careers. So we have to prove our medical knowledge and skill, and that means facing our nightmares - all the incredibly complex diseases that preoccupy us at test time, but which are only rarely seen in the field. We have to be on our guard and watch for the signs carefully, without becoming alarmists who forget to rule out common things and ignore Occam's Razor (thus panicking patients and annoying attendings). 

What worst-case scenarios do you fear in your job? In your life? I'm not talking about stuff like death and safety that most people share - what are the ones specific to you? What do you think about and then have to stop and remind yourself that that is not the only scenario, or that there is an easier way?