ISTJs always stick to their beliefs and values. They trust their own judgement above all others, even when they are wrong. Because of this ISTJs can be inflexible and stubborn. Others may see ISTJs are too forceful in their decisions.
Because ISTJs are so idealistic when it comes to their values, they may be unaccepting or judgmental towards others who do not share those values. They may seek out friends who are like themselves, and/or try fruitlessly to change others.
Because ISTJs are so focused on logic and reason, it may be challenging for them to deal with emotions. They have trouble expressing their emotions, as well as feeling empathy for others.
ISTJs thrive on structure and routine, and may have difficulty in new or unusual situations. They place a great deal of value on tradition, and change can make them very uncomfortable. ISTJs would much rather stick with a tried-and-true method, rather than a new idea that may not work.