Fear can prevent someone from moving forward or from trying certain sexual acts. Those fears usually come from unfamiliarity or inexperience, or from bad experiences from the past, or from bad associations that came from watching, reading, or being told that some act is dangerous, painful, unhealthy, or humiliating. Those fears commonly cause some people to tense up or shy away.
Most fear is created by anticipation and by projecting thought forward. In a moment of true pain or danger there would be no anticipation, just action or reaction. Fear can also be indirect. A sub may not fear the act itself, but fear the capacity of the Dom to do it correctly and safely. Fear also comes afterwards when you think about what could have happened.
The same kind of fear reaction can occur when about to engage in something new. The deep instincts we have of fight or flight cause us to tense our muscles.
An experienced Dom must know when to use fear and when to avoid it. He can use fear, even provoke it, with the intention of tensing the sub and heightening her senses, stimulating and intensifying the experience. He may also use trust, care, comfort and orientation to calm down, prepare and relax the sub prior to a challenging act or situation.
Those are moments when I don’t advocate the use of alcohol or drugs at all. If you can’t calm down someone to do something while sober you shouldn’t try it with her drunk either. A [pseudo]Dom that needs to intoxicate a sub to have his way is a faker and potentially a criminal. I am not against the use of alcohol or even drugs as recreational items and to have fun at other moments, but during sex in general and BDSM in particular.
Interesting question posted on 
Everything I’ve experienced has led me to believe that when it comes to BDSM, there are two main categories of people: there are kinksters, people who enjoy the lifestyle and find pleasure in certain aspects of it; and then there are a smaller category of people who seek it out because they recognize in themselves an innate need to dominate or submit. It doesn’t need a name or a definition. It is just there, lurking in the subconscious, waiting to be unleashed on the conscious mind. The latter category of people are the ones I am most interested in, as it is the category I belong to.
There are several aspects to that like the different social roles (alphas, betas, etc), the biological drive, etc. But I think one new aspect is very influential in modern society. I heard from several friends that are Doms and Dominatrix pretty much the same story with little variation: that when someone is in charge and important and full of responsibilities in the “real world” that person would have a strong drive to then prefer the opposite in their sexual life, hence their strong drive to become sexually submissive.
Individuals who submit control of a large percentage of their day-to-day life to a dominant partner, or who submit within a formal set of rules and rituals are sometimes referred to using the term slave, which is distinctly different from the historical use of the term, and the practice of this type of consensual sexual slavery is different from the historical practice of slavery.
I appreciate a deeper level of sensual connection. An intense sensual awakening that only happens when lovers trust each other and are engaged in discovering what pleasures them the most, and what pleasures their lover.