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.
ISTJs at their best are dedicated and pragmatic individuals who understand what it takes to get the job done and put their best effort into the tasks they choose to undertake. They are extremely knowledgeable about the inner workings of systems and procedures in the world, in large part because they take the time to truly learn how to do things and observe how everything works and fits together. They often seem to have an amazing memory to others and are often skilled at making connections between present and past experiences, or events that others miss. Their primary interest lies in developing a mental “owner’s manual” for the world, indexing every necessary piece of information in order to become as efficient and effective as possible.
ISTJs tend to believe that the best way to understand the world is to observe the collection of objective facts that humanity has accumulated over time, relying on these as trustworthy pieces of information. They do not trust whims and fashions, but prefer to find out what works and what’s true based on the body of scientific and practical knowledge that already exists in the world.
However, it is also important for ISTJs to spend time on their own desires and beliefs and the values they hold dear. While predominantly logical, most ISTJs also have a sentimental side, which they tend to keep to themselves and only explore in private. It is this side, among other things, that allows them to find personal meaning in their work.
Well-developed ISTJs are often very flexible with regards to considering their options, and understanding the world not merely as a fixed entity, but also as a malleable object that, through their own acumen and expertise, can be shifted and adjusted to their will.
ISTJs tend to be more reliable and effective than other types, making sure that things get done in the right way, or that the people who are making judgments and decisions are doing so based on the best information possible. For the same reason, ISTJs rarely allow themselves to get sidetracked by passing whims, and they are not easy to distract from the bottom line or the essential task at hand.
ISTJs tend to be very good at taking objective facts and analyzing and evaluating them in order to predict the long-term, real-world possibilities they allow for. If a thing doesn’t make sense to them, there is a good chance that thing is somehow overhyped and will never be able to work in the real world. Hence, for this reason, many ISTJs make good investors, bankers and venture capitalists.
ISTJs do not enjoy navigating the world of human interaction, and will often find themselves annoyed with people’s emotional irrationalities or willingness to chase after the latest fad. Although they may, in situations where they really put their mind to it, make allowances for the imprudence of others, and learn to work around them, this mode of functioning is rarely preferred by the ISTJ. In general, they prefer to work with information and parameters which can be proven to be objective and correct and which allow for clear ways of keeping score of failure or success.
To summarize, ISTJs are grounded, effective and rational individuals who seek to understand the in-depth workings of whatever they chose to engage with. They often value effectiveness and logic and they typically have high professional standards. They can often be meticulous with regard to the quality of a piece of work or performance, though they are not as much perfectionists as they are simply rationalists, purposefully drilling down to understand how a given performance can be improved in depth. When they balance their very high standards with a nod towards their personal sentiments and values, ISTJs can become extraordinarily successful individuals, performing great feats of accomplishment through sheer determination that leave the rest of the world marvelling in awe.