Blocks are used as a last resort when all else has failed, such as deflection or avoidance (sidestepping or ducking) or leaving. Even then, the block may fail. When a block fails, you get hit. Even if a block works, your blocking arm or leg may be injured. Blocks are violent—it is force is meeting force. Blocks require a lot of energy, they stiffen the body, and they cause mental as well as physical stress. You may rely on blocks against people who have shorter leg or arm reach, have much less body mass than you, are much less as strong as you, or who are frail for some reason; however, as a general rule it is better to evade than it is to block.