Estimated to be between 7 and 10 percent of the American population
Private, quiet, and generally reserved, ISFJs may be slow to warm and are selective about whom they reveal their gentle, caring nature to. Most ISFJs are quite cautious and tend to be initially hesitant about meeting new people. Not usually initiators of interaction, ISFJs usually like to wait and watch new situations before getting involved. With their families or close friends, however, they are generally cheerful and affectionate. They are happiest playing one-on-one or in small groups with other kind and friendly children like themselves. They do not like mean or rude people and easily get their feelings hurt when others are rough or speak to them in harsh tones. They are especially unnerved by aggressive people and will typically avoid them after even one unpleasant interaction. They tend to be thoughtful, loyal, and considerate friends and often maintain cherished childhood friendships for many years, even into adulthood. They want to please those they care about and often like to be helpful around the house.
ISFJs are very realistic people, most comfortable knowing exactly what is expected of them in clear and explicit terms. They tend to take things very literally, so they may become confused or frustrated by vague directions or answers. They may insist that their parents tell them exactly what is going to happen and at precisely what time. They tend to accept things at face value, so they may be at a loss to decipher hidden meanings of themes. ISFJs are often highly discriminating about sensory experiences, from being selective eaters to choosy dressers to recoiling from unpleasant textures or odors. They tend to hold very clear and strong opinions about anything that affects them personally and are often unwilling to compromise their values or decisions. They can sometimes have a rather black-and-white perspective and may be skeptical about new or different ideas.
ISFJs are at their best when they have a routine and structure in their daily lives that is consistent and reliable. In fact, they may resist change and become rigid about the way things must be. They usually like order around themselves and maintain tidiness in their personal space, from organized dresser drawers to toys that are carefully put away after playtime. They may want to stay clean and appropriately dressed and groomed. Usually, they are very careful with their schoolwork and take all of their obligations seriously, wanting to do their very best on each assignment. Once they start a project, they want to work diligently and steadily toward finishing it, without interruptions. They don't like to leave tasks undone and take great pride in their accomplishments. They are respectful of authority and are comforted by knowing and obeying the rules.
ISFJs have a tendency to worry often about safety and security issues or about possible tragedies befalling people they love. They take all loss very personally and may grieve for extended periods of time when a family member or beloved family pet dies. They may initially say they don't like something for which they have no frame of reference and refuse to try a new activity, food, or approach. They may be helped when a parent patiently gives them plenty of realistic information about what a new experience will be like and then reminds them of other experiences from their past that were similar. These efforts usually give ISFJs enough information to help them become comfortable enough to give the new experience a try.
[Source: Nurture by Nature: Understand Your Child's Personality Type – And Become a Better Parent by Barbara-Barron Tieger and Paul D. Tieger]