An adventurer can practice barehand attacks in order to improve their skill in that style attack. An unproficient person has a good chance of making an error when using thier fist as a weapon. Errors such as hitting yourself, hitting the wrong target, or just missing all together are common when you aren't proficient. By contrast, the expert has a better chance of hitting, and is also able to direct his shots toward more "critical" spots. Critical blows do upwards of twice the normal damage as a regular blow would. Any fool can use a weapon, but it takes training and practice to wield a weapon well and not be more of a danger to yourself than your target.