It is poorly understood, though, what ultimately connects these emotional experiences to sexual gratification, or how that connection initially forms. Dr. Joseph Merlino, author and psychiatry adviser to the New York Daily News, said in an interview that a sadomasochistic relationship, as long as it is consensual, is not a psychological problem:

Its a problem only if it is getting that individual into difficulties, if he or she is not happy with it, or its causing problems in their personal or professional lives. If its not, Im not seeing that as a problem. But assuming that it did, what I would wonder about is what is his or her biology that would cause a tendency toward a problem, and dynamically, what were the experiences this individual had that led him or her toward one of the ends of the spectrum. It is usually agreed on by psychologists that experiences during early sexual development can have a profound effect on the character of sexuality later in life. Sadomasochistic desires, however, seem to form at a variety of ages. Some individuals report having had them before puberty, while others do not discover them until well into adulthood. According to one study, the majority of male sadomasochists (53%) developed their interest before the age of 15, while the majority of females (78%) developed their interest afterwards (Breslow, Evans, and Langley 1985). The prevalence of sadomasochism within the general population is unknown.
For Deleuze, insofar as desire is a lack it is reducible to the "Look".Finally, after Deleuze, René Girard included his account of sadomasochism in Things Hidden Since the Foundation of The World (1978), making the chapter on masochism a coherent part of his theory of mimetic desire. In this view of sadomasochism, the violence of the practices is an expression of a peripheral rivalry that has developed around the actual love-object. There is clearly a similarity to Deleuze, since both in the violence surrounding the memory of mimetic crisis and its avoidance, and in the resistance to affection that is focused on by Deleuze, there is an understanding of the value of the love object in terms of the processes of its valuation, acquisition and the test it imposes on the suitor. Modern psychology
There are a number of reasons commonly given for why a sadomasochist finds the practice of S&M enjoyable, and the answer is largely dependent on the individual. For some, taking on a role of compliance or helplessness offers a form of therapeutic escape; from the stresses of life, from responsibility, or from guilt. For others, being under the power of a strong, controlling presence may evoke the feelings of safety and protection associated with childhood. They likewise may derive satisfaction from earning the approval of that figure (see: Servitude (BDSM)). A sadist, on the other hand, may enjoy the feeling of power and authority that comes from playing the dominant role, or receive pleasure vicariously through the suffering of the masochist.