Sensing the subtle is how sensitive people come up with all the wonderful insights they are capable of. Dr. Aron describes it as follows:
Most of the studies already cited required perceiving subtleties. This is often what is most noticeable to us personally, the little things we notice that others miss. Given that, and because I called the trait high sensitivity, many have thought this is the heart of the trait. (To correct this confusion and emphasize the role of processing, we used “sensory processing sensitivity” as its more formal, scientific designation.) However, this trait is not so much about extraordinary senses— after all, there are sensitive people who have poor eyesight or hearing. True, some sensitive people report that one or more senses are very acute, but even in these cases it could be that they process the sensory information more carefully rather than having something unusual about their eyes, nose, skin, taste buds, or ears. Again, the brain areas that are more active when sensitive people perceive are those that do the more complex processing of sensory information. Not so much the areas that recognize alphabet letters by their shape or even that read words, but the areas that catch the subtle meaning of words.
Our awareness of subtleties is useful in an infinite number of ways, from simple pleasure in life to strategizing our response based on our awareness of others’ nonverbal cues (that they may have no idea they are giving off) about their mood or trustworthiness. Of course, on the other hand, when we are worn out we may be the least aware of anything, subtle or gross, except our own need for a break.
Sensitive people get bogged down not only because of the volume of information that they take in but also because sensing the subtle in all the information they encounter adds a lot of mental and emotional processing to their workloads. As a result, they use deep processing to deal with both the volume and subtlety of the information they take in. The combination can be difficult to handle unless a sensitive person has a strong health foundation and good skills in processing and self-pacing.
 Author’s Note, 2012 for The Highly Sensitive Person, 9/6/2012, link.