Who are ISTJ? ISTJ stands for Introversion (I), Sensing (S), Thinking (T), Judgment (J). 13 percent of the world population is considered as ISTJ Personality, making it the most common Myers–Briggs personality type. The ISTJ personality type is believed to be dependable and patient people with characterizing qualities of honesty, reasonable rationale and a vigorous sense of obligation. ISTJs are ...