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 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 officiation 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.