Woo FF is becoming a pro on this, I would have said the exact same thing almost, but I'll just add a little extra info:
ISFP = Fi (holding strong beliefs & values close to the heart) + Se (living and acting in the present moment). This means with any situation that faces you, first thing you will do is evaluate it depending on how it affects your morals. Does this situation collide painfully with your beliefs? It does? I must act on it NOW. No? It's safe? Good, because they would have been sorry if it wasn't. To be fair ISFPs are not blunt individuals, they are actually very caring, and do take things quite deeply personally. They come across very introverted to others and like in the name, they love to channel their feelings through artistic means. Meaning ISFPs come across as very timid, quiet, but friendly too, and as you get to know them more you see a much more outgoing side to them, but their Fi means that they sometimes are a bit stubborn too and may not always go along with what you want to do.
ISTJ = Si (comparison of new events to past events and building on experience) + Te (the use of external, proven logical data). When you put the two together in that order, this is what happens. You hear of a new situation, a new event, that may remind you of another experience in the past, then you evaluate it based on what you learned from that past experience and what that past experience has proven to you now by logical standards. ISTJs are constantly comparing their past experience to what the world has already taught them and what they already know. ISTJs are very serious, but hard-working and loyal people. They like to challenge others and they come across even more introverted than an ISFP.
tl;dr ISTJ & ISFP have similarities, yes, but it's still about how you feel underneath how you act. ISFPs have strong morals that they will not let you break through, if you try they'll put you in your place. ISTJs learn logically from their past experience and believe that reflecting on something and learning from that is the best way to face a problem.







