The overall idea is that Te and Si are there as semi-conscious checks on how Ne/Fi will go about their normal business. The Ne/Fi is far, far more conscious and in control, but (presumably) there's still those shaping semi-conscious backgrounders.
For you see, I believe I have seen Si at work in young ENFPs. They routinely make clear claims of a wish for a steady, quiet life. And I'm like, woah, what the--, who--, what's going on here? My hypothesis is that's Si reaching up its staid black tentacles to squeeze Ne/Fi into some kind of realistic shape. In 19-year-olds.