People always wonder how a tactical vest with just Kevlar can stop a bullet but not a knife. Here is a simple explanation. The ogive, or tip, of a bullet is slightly rounded and upon impact will compress under the pressure. This compression will make the round flatten like a plate and disperse the Energy throughout the vest. A knife has such a sharp angled tip that it is classified as Focused Energy. Think of a soda bottle. When the liquid from within the bottle comes out it is poured through the opening which is smaller than the rest of the bottle. This allows the liquid to flow out of the bottle in a small stream "focusing" the liquid into one point. Focused Energy works the same way as the liquid and is sometimes referred to as "bottle necking the energy". In martial arts focused energy can be practiced and can take years to understand the dynamic concepts.