In a truly professional sales environment, everyone must win: the client, the company, and you.
This doesn't mean that everything will go perfectly for everyone. Some form of compromise is necessary (yes, even from the client). The goal has to be "the greatest good to the greatest number."
What scares you?
For most, it is fear of failure in some form. Fear of failure is natural, human, and even beneficial when examined properly. Most people don't delve into the root causes of why they are afraid, and only deal with the external emotions generated from their fear.
Fear could signify that the action you are taking needs tweaking, or that you need a different strategy.
There is a defense mechanism embedded in fear that could be your "still small voice" warning you that you are not ready...yet. How do you know the difference between the early warning system and just good ole "I'm scared?" Most people know intuitively which is which, but deep personal introspection and not just surface skimming will help you deal with the "root" and not just the "fruit."
Fear: a state of inability to perform a function
Do you fear because you think something is not possible? The "4- Minute Mile" was once thought impossible until Roger Bannister ran it in 1954. Since then, many have done it, including high school runners! Take the It's Possible Test - does your industry allow for you to earn the income you require to achieve what you desire? Is anyone in your industry earning that income? Yes? Yes? Then it is possible and your fear should be knocked down a peg!
The real question is: Do you feel worthy?
The "4 Minute Milers" may have experience you don't have (then have some experiences). They may have knowledge you don't have (then get the knowledge). They may be working harder than you; Shut up (smile!), wake up, and get busy! They may be more talented than you, so... practice, practice, practice!
Your ultimate fear of failure in sales is due to perceived inability.
Each area you could review can be developed by dedication: product knowledge, prospecting activity, presentations, and effective closing. The diligence you provide will direct you to experiences that help develop necessary skill that will lead to success!