Why exactly are these types so different? I think I notice it a lot, but I still can't figure out why.
I've recently began speaking more closely with an INFP (well I have typed her so, although it's not been self-confirmed) and she seems less aimless, less cautious, more outspoken, more quick to stand up for her rights, much less flexible in her sense of self, and not as visibly sensitive (yet still crazy understanding and willing to forgive easily). Overall, she seems much more sure of herself. I only learned about how much things like criticism and disapproval really affect her when she self-disclosed it during discussions, and I was very surprised. At times we seem worlds apart, although we still connect to each other through our outlook on the world (in terms of Feeling) and things we hope to accomplish in life, and that is always an energizing experience. I feel understood. Unlike with the IFJs I know, there are rarely any complaints about the discussion not going beyond a personal level.
On a totally different note, I have a good friend who is ISFP, almost a complete turn around from the INFP above, and we get on extremely well. About the only glaring differences are that she is far more optimistic and pleasant. We are both more confrontation avoidant, more apt to tolerate a problem longer before we fix it, more vague about our opinions, and we both show our sensitivity more. The differences between ourselves and the INFP can be so pronounced that it makes me wonder if both I and she are actually ISFJs (even though there are many factors that simply do not fit) rather than Fi types.
However, these kinds of differences tend to be reinforced by online descriptions. Is it that Se-Ni and Ne-Si really do make that big of a difference, or have I simply mistyped the first girl?