ISFJs make very compassionate company. With Introverted Sensing (Si) as their primary function, otherwise known as subjective sensation, and Extroverted Feeling (Fe) as their secondary function, otherwise known as objective ethics, ISFJs are usually in their heads or spending time with friends and loved ones. They are a naturally submissive personality and can be very easy going. Their moods are slow moving and not easily changed. With Si as their primary function, there is always a sort of homeostasis the ISFJ is striving to maintain, both emotionally, and physically.