From an evolutionary survival standpoint, fear of the unknown is not necessarily a bad thing. If the choices are, "assume this unfamiliar plant is poisonous" or "assume this unfamiliar plant is not poisonous," the first choice is definitely the less risky one. This becomes a problem, though, when we generalize "this unfamiliar plant may be poisonous" to "all unfamiliar plants are certainly poisonous, and may be spraying noxious fumes directly into my nose at this very moment!" This example may sound silly, but if you think about it, we turn specific risks into general "danger" all the time -- usually by refusing (or perhaps just forgetting) to confront the real risk.
A friend of mine, who is an internationally-known expert on security, just recently wrote a great article about this very topic. He cites a tendency of people to respond more readily to defined risks (for example, purchasing insurance that specifically covers an act of terrorism against an aircraft) than to general ones (for example, purchasing insurance that covers any emergency or accident that occurs during one's flight). Part of this is a direct result of our fear of the unknown. If we can define the threat, we can respond to it, and in this way we can exert some control. Maybe, if we respond to enough specific risks, we'll cover enough of the bases to have a statistical advantage over the things we haven't considered. Or perhaps it's more insidious than that -- we try to protect ourselves against the specific in order to avoid having to imagine what else could go wrong.
When you avoid a particular situation - for example, making sales calls for your business - this is what's happening. You "protect yourself" from making the call (which is a specific action) and avoid having to imagine what might happen if you did make it (a wide, and as yet undefined, range of possible outcomes -- including some that are very positive!) You've gained the security of staying in your comfort zone, but you've lost the opportunity to enjoy a favorable result.
What risks are you avoiding right now? Take a moment to reflect on your current "risk profile." Are you avoiding an actual "poisonous plant," or are you letting yourself be beaten by a totally undefined foe? What does the worst-case scenario really look like? Will someone die if you are not completely successful? Even if something big, like your job or an item of your property is at stake, how big a deal would it be to lose it? And how likely is that, if you're being honest and realistic about the risk? Take the time to define the risk in concrete terms, and determine what all your options are. Be sure, in this process, to include all the possible good outcomes as well! Once you have honestly assessed all the sides of the situation, if you can honestly say the risk is too great, then let go of it and don't look back. But if the risk is manageable, as most risks are, make a plan for how you will manage it. Your plan will give you direction, focus, and confidence -- the three tools you need to stop fear in its tracks.