When reading type descriptions, remember that "type portraits" can never accurately describe all people of a given type. Descriptions and portraits like these can only describe the types as they typically are.
ISTPs are cool-headed problem-solvers who improvise and don't mind taking risks. They're realistic and factual and often exhibit an enviable calm in an emergency. ISTPs often excel at meeting challenges head-on and overcoming them. They are usually independent and they don't mind going their own way. In fact, they often crave the freedom to follow their own rules rather than going along with the rules of "the system." When faced with a problem, they cut straight to the chase, and if they don't understand why a given rule is there, or what purpose it serves, they are likely to disregard it as they see fit. In the eyes of others, ISTPs may simply appear dismissive of such rules, but inwardly there is a process of logical analysis that has determined which of the rules are superfluous and which are needed. However, because their method of separating the wheat from the chaff is more bare-boned and logical than most, their judgment about which rules that are unneeded tends to be more extensive than most.
ISTPs tend to have interests that are oriented towards real-world tangibles and factual results. They care about results in the real world and they typically do not see the point of fluffy talk for its own sake. Many ISTPs are curious about technology and mechanical equipment and they will not rest until they understand how something works. ISTPs tend to enjoy physically interacting with the world, using their problem-solving skills to manipulate objects and master them. ISTPs tend to have little patience for theoretical foppery "that never leads anywhere." ISTPs who are academically inclined will therefore tend to go for subjects that also have a practical application (such as medicine and finance) while avoiding subjects that dabble in theory for theory's sake without producing many real-world results (such as philosophy or literary theory). Economical with their words and realistic to a fault, ISTPs tend to have little patience with pompous words and subjective observations that in the end are backed up by nothing more than more pompous words and more subjective observations. They tend to believe that the work should be able to speak for itself.
ISTPs have a utilitarian mindset and are often mercilessly realistic about what works and what doesn't. As such, ISTPs can be said to be more clear-headed than other types: If a thing doesn't work, they adapt and make it work. The ISTPs of this world are not to be found among those starry-eyed dreamers who keep pushing the same boulder up the hill only to have it roll down again as soon as they let go. To an ISTP, a project that failed and is accompanied by a long and detailed explanation of why it should have worked is often no better than a project that simply failed.
ISTPs prize freedom and independence - especially their own. But they also tend to respect the sovereignty of others and they generally dislike imposing themselves on others, meddling in other people's affairs, or telling them what to do. Indeed, as one ISTP once noted, "the most important thing in life is not to interfere with somebody else's life." Hence ISTPs tend to resist attempts to control them, just as they usually refrain from trying to control others.
This zest for independence lends the ISTP a charisma that is imbued with aloofness and self-sufficiency, yes, perhaps even of perceived unfriendliness. The ISTP's drive for self-governance also means that in the role of leader, an ISTP will usually have an easy time being hands-off and empowering their subordinates with the level of freedom and flexibility that they need to get the job done. With regards to leadership, an ISTP is truly the type of leader that exposes himself to fire along with his men - the leader who leads by example rather than by giving long and flowery speeches from the safety of the back seat.
ISTPs are logical and unsentimental. Along with the ESTP, they are the type that is the most free of illusions about how the world works. They tend to hang back, quietly observing what is going on around them. While in this mode they also have a keen eye for opportunities, and when one presents itself, they seize the moment and pounce. Hence it has often been observed how ISTPs almost seem to have two different personalities: One that is analytical and quiet, hanging back and going over things in his own head. And then another, which is more action-oriented, adventurous and risk-taking; a cool-headed problem solver that springs to action when others are lost.
ISTPs are naturally focused on the bottom line and the real-world consequences of the matter at hand. Cool-headed and logical, they're well-equipped to handle conflict and criticism, but also somewhat private and impersonal and may at times appear aloof to others. However, this aloofness rarely stems from arrogance, but rather follows from their clear-headed focus on the facts and their preference for cutting straight to the chase. The ISTPs of this world are usually the first to call a fraud when they see one and the last to be suckered into a project whose meaning is unclear.