I know a couple ISTps, an old boyfriend and my mom, who are extremely outgoing. I was really scratching my head about their types for a while, until Peter said that my mom is INTp. INTp doesn't make sense for her because she has shitty Ni, but I suggested ISTp and he agreed. Later she tested ISTp, and the more I learn about socionics, the most sense it makes. The other one tested ISTp and said that the description fits him very well. I compared his behavior to my mom's and it all made sense...
Both of these ISTps are very outgoing. They try to be sun shiney and very friendly, but it's horribly awkward and embarassing and they are generally not well liked. My mom has a bit of an easier time because she has friends from church who do the fake sunshiney thing as well to some extent and really relate to her, like an INFj (she's also good friends with his ENFp wife).
The 4th function is a conscious function... it's one we can use but cannot control. There are a lot of people who overcompensate for their 4th function, and these two are perfect examples.
Has anyone else observed this behavior in ISTps?