Answer:
It should be as hard or harder than your limits. It is designed to find your limits and try to push you to the edge of what you can endure (or cause you to quit). It is mentally and physically challenging. It is designed to be hard, so you can be prepared for what will be expected of you. It is much less painful to endure a training sergeant yelling at you, cram for evaluation events, and put up with the discomfort of a little physical exercise than it would be to catch a bullet in your chest or head because you were not prepared. Yes, it is hard! That is the point!