You're not alone. Many of us are insecure with some facet(s) of life. It's a rare individual who is comfortable about everything including who he(she) is. It's a rare individual who is unaffected by external events. Only ascended individuals can claim to do both. And very few of those individuals are able to do both and maintain humility.
Fearing the worse case scenario about recruits allows you to not be disappointed should the worse case happen. It's a defense mechanism. Usually we employ this mechanism when we have put our hopes up in the past and had them severely disappointed. It could be a one time event, severe or not severe, or it could have been multiple events, severe or not severe. The development of a defense mechanism is individualized but in every case there was a threshold of pain that took place that the brain determined should not be allowed to happen again.
Often these defense mechanisms take place in the neural networks within our brain that we categorize as the subconscious. A good part of that activity has now been shown by MRI's to be active in the Amygdala part of the brain. This part of the brain has a strong influence on behavior, much stronger than the conscious or cortical parts of our brain. This is why it is difficult to overcome our fears.
If you want some more ideas on how to deal with this let me know.