ISFJ + INFJ

You might think these highly sensitive people would have an easy time understanding each other because they share (I)ntroversion, (F)eeling and (J)udging, this is not necessarily so.  Even though they differ by one letter, they perceive the world in vastly different ways. The INFJ is the rarest type, while ISFJ is the second most common, and this one letter difference keeps them constantly guessing as to what the other is thinking and clashing when it comes to long-term planning and lifestyles. 

Fortunately, the similarities outweigh the differences, and these issues may be resolved with maturity and a willingness to understand one another's individuality.