ISTJ: The Duty Fulfillers, the Inspectors, the Examiners
ISTJs have an excellent work ethic. They are usually willing to do just about anything that needs to be done. However, if the work does not seem useful the ISTJ will lose interest and the typical devotion so common among this type.
ISTJs are driven by a sense of duty. They look to such obligations as a blueprint for life decisions. Morals and values appear very clear to the ISTJ. ISTJs typically will not break the law, nor most rules and regulations. Even when popular opinion says that rules can be bent, if the ISTJ sees principle in the rule they will stand firm in conviction.
ISTJs trust facts, hard data. They speak directly and straightforwardly, but on rare occasion like other I’s. ISTJs have a perspective that is sometimes likened to an umpire- in any given situation, they are able to make those difficult calls. They are not easily distracted from the truth. ISTJs are able to develop fine precision and make excellent employees; trustworthy, dependable, hardworking, they do not question authority. But when an ISTJ is asked for their opinion, they will state it clearly, matter-of-factly, and will not mince words however harsh the facts may be.
ISTJs are excellent companions. They are not only devoted, rarely straying from commitment, and loyal individuals. ISTJs also have a surprisingly passionate side. ISTJs can be romantics in love matters. ISTJs work hard long past due vacations, and often will not take a vacation even after they very much deserve one. ISTJs benefit from a companion who encourages them at such times to let loose and enjoy the fruits of their labors…at least once in a while. However, ISTJs are not easily persuaded in such matters.
ISTJs do not have patience with theories, unless the theory is easily obtainable to provide usefulness. The ISTJ must see the practical use in the beginning.
References: Wikipedia, PersonalityPage, Knowledge of personally known ISTJs