A quick passage from Spetsnaz by Viktor Suvorov; (Emphasis is mine)
“A spetsnaz soldier knows that he is invincible. This may be a matter of opinion, but other people’s opinions do not interest the soldier. He knows himself that he is invincible and that’s enough for him. The idea is instilled into him carefully, delicately, not too insistently, but continually and effectively. The process of psychological training is inseparably linked to the physical toughening. The development of a spirit of self-confidence and of independence and of a feeling of superiority over any opponent is carried out at the same time as the development of the heart, the muscles and the lungs. The most important element in training a spetsnaz soldier is to make him believe in his own strength.
A man’s potential is unlimited, the reasoning goes. A man can reach any heights in life in any sphere of activity. But in order to defeat his opponents a man must first overcome himself, combat his own fears, his lack of confidence and laziness. The path upwards is one of continual battle with oneself. A man must force himself to rise sooner than the others and go to bed later. He must exclude from his life everything that prevents him from achieving his objective. He must subordinate the whole of his existence to the strictest regime. He must give up taking days off. He must use his time to the best possible advantage and fit in even more than was thought possible. A man aiming for a particular target can succeed only if he uses every minute of his life to the maximum advantage for carrying out his plan. A man should find four hours’ sleep quite sufficient, and the rest of his time can be used for concentrating on the achievement of his objective.
…It is a philosophy which cannot be put into words. The soldier grasps it not with his head, but with his feet, his shoulders and his sweat. He soon becomes convinced that the path to victory and self-perfection is a battle with himself, with his own mental and physical weakness. Training of any kind makes sense only if it brings a man to the very brink of his physical and mental powers. To begin with, he must know precisely the limits of his capabilities. For example: he can do 40 press-ups. He must know this figure precisely and that it really is the limit of his capacity. No matter how he strains he can do no more. But every training session is a cruel battle to beat his previous record. As he starts a training session a soldier has to promise himself that he will beat his own record today or die in the attempt.”