ISTJs are often called inspectors. They have a keen sense of right and wrong, especially in their area of interest and/or responsibility. They are noted for devotion to duty. Punctuality is a watchword of the ISTJ. The secretary, clerk, or business(wo)man by whom others set their clocks is likely to be an ISTJ.
As do other Introverted Thinkers, ISTJs often give the initial impression of being aloof and perhaps somewhat cold. Effusive expression of emotional warmth is not something that ISTJs do without considerable energy loss.
ISTJs are most at home with "just the facts, Ma'am." They seem to perform at highest efficiency when employing a step-by-step approach. Once a new procedure has proven itself (i.e., has been shown "to work,") the ISTJ can be depended upon to carry it through (even at the expense of their own health).
ISTJs are easily frustrated by the inconsistencies of others, especially when the second parties don't keep their commitments. But they usually keep their feelings to themselves unless they are asked. And when asked, they don't mince words. Truth wins out over tact. The grim determination of the ISTJ vindicates itself in officiating at of sports events, judiciary functions, or an other situation which requires making tough calls and sticking to them.
His SJ orientation draws the ISTJ into the service of established institutions. Home, social clubs, government, schools, the military, churches -- these are the bastions of the SJ. "We've always done it this way" is often reason enough for many ISTJs. Threats to time-honored traditions or established organizations (e.g., a "run" on the bank) are the undoing of SJs, and are to be fought at all costs.