“How does one man assert his power over another, Winston?”
Winston thought. “By making him suffer,” he said.
“Exactly. By making him suffer. Obedience is not enough. Unless he is suffering, how can you be sure that he is obeying your will and not his own?”
– George Orwell, Nineteen Eighty-Four
If you're into pain, you can whip yourself. If you're into chastity, you can lock yourself. If you're into breath play, you are physically capable of playing solo. (For the love of all that's kinky, please don't ever do breath play solo.)
A slave doesn't need a master to be a slave. Of course it's different with a master, and of course there are certain things you can't do on your own, but an unowned slave can scratch some of his slaving itch on his own. A master, on the other hand, is only a master relative to the slave. Whether you enjoy inflicting pain or holding keys or tying other people up, there has to be another person to play with. From a power perspective, this gives the slave a small advantage. In the fantasy land, it's easy to imagine a "computer master", probably programmed to be cruel and merciless and logical to a fault. The concept of a "computer slave", however, doesn't make much sense.
Outside of the fantasy world, relationships need to be consensual. Sure, the slave is often put into excruciating positions, suffering from pain or humiliation, but that's only because he asks for it, and he only asks for it because he likes it. If the master is only giving the slave what he wants, is the master really the one in power, or is he simply providing a service?
This is the paradox of submission in a power exchange relationship. For the relationship to be healthy, the slave has to have more power, at least on some level. Does this mean all power exchange relationships are doomed by definition? Not really; we have a few outs.
Out #1: the power dynamic stays on a surface level. Like a mountaineer who keeps braving the elements, some things are painful on one level and entirely satisfying on another. Both people in the relationship understand this, and they're just having fun together by giving each other what they need. It's like a personal trainer pushing an athlete to his limit. The athlete enjoys the challenge and the trainer enjoys being a mentor. In a relationship, we call the trainer "master" and the athlete "slave", because one is giving orders and the other is taking them, and because one is inflicting pain while the other is suffering it, but they're really equals on all levels but one. This is the most common dynamic if people gather together for a "session" or a "scene".
Out #2: it's only a power exchange in your head. Like watching a movie, we suspend our disbelief to indulge in a fantasy. The slave knows full well that he can refuse any order at any time, but the fun would be spoiled and everyone goes home upset. The master knows the slave knows full well that he can refuse any order, so likes and dislikes and hard limits are discussed in advance. The two people are equal in the real world, but they're engaging in a fantasy where the master has the power. It's like starring in your own movies, and if a balance is found, this suspension of disbelief can go on for a long time, and it can feel very real.
Out #3: the slave enjoys the abstract concept of losing power, instead of specific ways of being vulnerable. This means the slave is not specifically into rope bondage, or chastity, or corporal punishment, but it turns him on to be ordered around. The slave could be ordered to do something he genuinely doesn't want to do, but his very reluctance is the trigger for his arousal, and that arousal will push him to follow the order despite his reluctance. This is an even more delicate balance, and it's often the master's responsibility to maintain this balance, because the slave can get into a headspace where he loses track of what he's being asked to do, only to feel he's been pushed too far later on. The master needs to be careful not to abuse the slave's trust, but the slave's suffering is also real.
Out #4: there's a deeper connection between the master and the slave. The slave's not enjoying what he's tasked to do, and he's probably not even enjoying the act of following orders, but he knows his master is enjoying giving the orders and watching the slave suffer, and he enjoys the fact that his master is enjoying it and wants to keep him happy. It's an act of self-sacrifice and devotion, and it takes a lot of trust and compatibility to achieve in a relationship. But when it works, both people will be tremendously satisfied.
All relationships are first and foremost a partnership. It doesn't matter how it appears to others; on a fundamental level, partners care about each other and help each other out. The paradox of submission is, in a healthy relationship, the slave's submission can't ever be truly total and without condition. But that's ok. Life isn't a fantasy, and by withholding a fraction of the power, the part you do surrender feels all the more gratifying.