It is not possible to go all out every workout. Using this training system, you plan your sessions so that the first is intense, with relatively high reps and sets, without use the heaviest weights. For the next session, you increase the weight, but still stay short of going all out. For your final workout, you go very heavy, keeping your reps low at 4 to 6 maximum per set.
By gradually building up your workouts during the week, you prepare your body to be able to handle the shock of very heavy weights toward the end. Progressive Overload is a commonly used power training principle whereby the higher reps and lower weights are swapped for lower reps and heavier weights as the week progresses. This enables you to be better able to handle the heavier weights at the end of the week. Progressive Overload is one of the Power Training Principles.