ISTP

An ISTP (Introversion, Sensing, Thinking, Perception) is a psychological type used in self-assessment typology instruments like the Myers-Briggs Type Indicator for individuals, who self-report preferences for introversion, Sensing, Thinking and Perception on the Myers-Briggs Type Indicator and similar typology systems based on the work of Carl G. Jung in Psychological Types.

Characteristics
ISTPs are disposed to analyzing situations and devising technical solutions, so that they can swiftly implement a functional repair. They tend to be interested in understanding the internal mechanics of things, focusing on efficient operation and structure. They tend to be observant to details; enjoy exploring new things; are easily bored in the absence of stimulation, but also highly adaptable to things around them, making them uniquely suited for high-risk activities (such as bungee jumping, hang gliding, racing, motorcycling, and skydiving), recreational sports (such as downhill skiing, paintball, ice hockey, and scuba diving), and careers (such as aviation, EMT, and firefighting).

Crafter Artisans (i.e. ISTPs) are masters at using tools of every type—artistic, technological and martial. Although they are introverts, they can be authoritarian in their interactions with others and can be forceful at influencing people, if needed. They are also disposed to handling dangerous social situations since their natural introversion limits their capacity to interpret social cues in the spur of the moment.

Cognitive Functions
Using the more modern interpretation, the cognitive functions of the ISTP are as follows:

Dominant: Introverted thinking (Ti)
Ti seeks precision, such as the exact word to express an idea. It notices the minute distinctions that define the essence of things, then analyzes and classifies them. Ti when paired with an extraverted, perceiving function (i.e. Se or Ne) examines all sides of an issue, looking to solve problems while minimizing effort and risk. It uses models to root out logical inconsistency. ISTPs live in a world of logic, on which they base their decisions.

Auxiliary: Extraverted sensing (Se)
ISTPs may sometimes seem to act without regard for procedures, directions, protocol, or even their own safety, but create strategies at a moment's notice. While their approach may seem haphazard, it is based on a series of mental models constructed over time through quiet action and keen observation with the world (Ti paired with Se). Due to this, ISTPs tend to perform at their peek in high-pressure and/or emergency situations, where their knowledge and experience can be immediately brought to bear — usually with the ISTP's characteristic unflappability. When others are just beginning to grasp the details of the situation, ISTPs are often (and sometimes from the perspective of those familiar with the ISTP, unexpectedly) resolving it. In personal matters, ISTPs enjoy self-sufficiency and take pride in developing their own solutions to problems.

ISTPs can often be an enigma to their friends or partners due to a combination of mixed social signals and a propensity to ignore everyone while deeply absorbed in a favored task. While ISTPs will readily participate in group activities that hold an immediate interest for them — and can be a great source of entertainment for all who participate — they will often eschew (either partially or entirely) the routine social interactions surrounding those group activities. Without intending any insult, the ISTP often concludes that such interactions — those that others might view as cordial or even expected — are redundant and superfluous; for the ISTP, the social event ended when the activity of interest concluded, and ISTPs are often uninterested in engaging in group-related small-talk. Should a topic of interest come up, the ISTP may suddenly re-engage the social group, only to disengage almost as abruptly when the topic passes. Sometimes in social gatherings and due to their innate desire to take in information on their surroundings at all times, the simple act of people-watching becomes sufficiently entertaining for the ISTP to, themselves, feel fully engaged by the social group; unfortunately, the often detached way in which the ISTP performs these observations can often be misinterpreted by others as an actively antisocial attitude.

Tertiary: Introverted intuition (Ni)
Such social characteristics often have the unintended consequence of making interpersonal relationships more challenging for ISTPs than other types. While friendships (which are typically based on a mutual interest in some concrete subject or activity) come much more easily for the ISTP since the relationship is straight-forward and can be clearly understood by the ISTP. Intimate relationships, on the other hand, tend to be far more difficult for the ISTP to form and maintain due to their inability to "wrap their minds around" an interpersonal dynamic based on subjective criteria that can vary from day-to-day or situation-to-situation. For the ISTP, actions speak much louder than words; so ISTPs tend to approach all of their relationships, including intimate ones, at face value — with the expectation that the other party is doing the same in return.

For example, ISTPs reason that flirty behavior is to be taken as an outright expression of interest; indifference is to be taken as an outright expression of disinterest. So either case can rapidly become a source of confusion and frustration for the ISTP when those of another type, such as ESTP or ESFP, casually engage in flirtatious behavior — or worse yet, hard-to-get behavior in an attempt to cultivate romantic interest through intrigue.

Inferior: Extraverted feeling (Fe)
Alternating between these opposing social behaviors — regardless of the true intent — would only serve to exacerbate an otherwise unclear situation for the ISTP, which produces inferior Fe insecurities including whiny emotional expressions or rigorous logic tainted by feelings of abandonment.

Ultimately, all of these social behaviors will often have an effect opposite to that intended, since the ISTP will interpret casual flirtation as interest when none actually existed; and indifference as disinterest rather than intrigue; and fluctuating expressions of interest as, at best, indecisiveness. This will lead to anxiety, as the ISTP despite their use of reason and logic is unable to appropriately connect with others emotionally, yet their usually-logical approach is tainted by emotional impulses manifested in a whiny and distrustful attitude of people in general.

Shadow functions
Later personality researchers (notably Linda V. Berens) added four additional functions to the descending hierarchy, the so-called "shadow" functions to which the individual is not naturally inclined but which can emerge when the person is under stress. For ISTP, these shadow functions are (in order):

Extraverted thinking (Te)
Te organizes and schedules ideas and the environment to ensure the efficient, productive pursuit of objectives. Te seeks logical explanations for actions, events, and conclusions, looking for faulty reasoning and lapses in sequence.

Introverted sensing (Si)
Si collects data in the present moment and compares it with past experiences, a process that sometimes evokes the feelings associated with memory, as if the subject were reliving it. Seeking to protect what is familiar, Si draws upon history to form goals and expectations about what will happen in the future.

Extraverted intuition (Ne)
Ne finds and interprets hidden meanings, using “what if” questions to explore alternatives, allowing multiple possibilities to coexist. This imaginative play weaves together insights and experiences from various sources to form a new whole, which can then become a catalyst to action.

Introverted feeling (Fi)
Fi filters information based on interpretations of worth, forming judgments according to criteria that are often intangible. Fi constantly balances an internal set of values such as harmony and authenticity. Attuned to subtle distinctions, Fi innately senses what is true and what is false in a situation.

Ti-Ni Loop
When the ISTP seeking a relationship decides to act, but is met with either awkward confusion when their advances are unexpectedly and summarily declined; or veiled disappointment because they failed to persist. The frustrated ISTP may move on, fallaciously concluding that any further effort in the face of such radically conflicting signals is a waste of their time. This "waste of time" thinking is a mere cognitive defence mechanism employed by the ISTP using tertiary introverted intuition (Ni). The ISTP misuses Ni to convince themselves that the future is cast in stone and so that the envisioned doom and gloom is inevitable, so why bother. The solution to this problem is not overindulge logic as a means to rationalize justify Ni, but to appropriately use auxiliary Se to chill and enjoy the excitement that truly comes from the unknown.

Se-Ni balance
Once a relationship is formed, however, ISTPs are content to let others live according to their own rules and preferences as long as the favor is reciprocated. Their Se provides a sense of chill that provides ISTP with an easy-going nature to balance the extremes of Ti and Ni. ISTPs will endure reasonable impositions without complaint; but if their "territory" is encroached upon, eroded, or violated, their quiet, easy-going nature is quickly abandoned in favor of stubborn, staunch, and uncharacteristically vocal defense of what they view as rightfully theirs. Such ISTPs are prone to childish, angry outbursts due to immature Se that is suppressed in an unhealthy environment. The Se impulses result from excessive reliance on Ti (i.e. using it to remain introverted when such is not desirable). For outsiders, this jumping between Se chill and Ti stubbornness creates a sense of unease. The ISTP is unknowingly manipulating persons because the other person, frightened that their ISTP friend or partner might get angry or violent, conforms to the ISTP, not wanting to experience their wrath due to loss of Fe control. In reality, ISTPs do not intend, nor want to intentionally manipulate others. It is just an unfortunate consequence of living in an environment where Ti and Se are not permitted to be used to their full potential. ISTPs can also learn to better control their anger through emotional intelligence training so that anger does not lead to yelling or violence.