Ransomed, like Laser says, you can usually figure out at least one or two letters for the majority of people. Usually people get stuck on either T/F or S/N, although any of the function pairs can be ambiguous.
One notable thing that happens when people age is that they become more well-rounded. I find it easier to type teenagers and young adults, but older people are starting to show signs of multiple functions and they can change what they use depending on the appropriateness of the situation rather than constantly relying on their primary or secondary to get them through.
This makes them harder to type... but that is actually a positive thing.
In our type arguments, there seems to be a LOT of debate about larger-than-life historical figures. At the positive end, you have someone like Jesus who used all of his functions seemingly well. At the negative end, you have (sigh) Hitler... I hate bringing him into it, but people argue incessantly about his type as well, leaving one to want to throw her hands up in the air and go do something fun (like eating Ben N' Jerry's? hmmmm....)
And then you have people like Uber, who deserve a category all to themselves, but anyhoo....
