In General Relativity, mass-energy causes space-time to curve, space-time causes mass-energy to move differently. Looking at either one alone results in an incomplete picture.
So it is with Te and Fi. Te causes Fi to change shape, Fi causes Te to move differently.
What we see is affected by the balance of Te to Fi. If Fi is stronger, then Te moves rather erratically, and Te barely affects Fi. If Te is stronger, Fi can curve almost into a black hole, with no light coming out.
If they're of comparable strength, then a third qualitatively different case arises. Te can be used to "sculpt" Fi, establish rules, teach Fi core principles to adopt. Fi in turn can be used to steer Te in accordance with the Fi core principles.
I'd ask for examples of this, but, um, I once started a thread asking what someone balanced in T and F would look like. About 20% of respondents replied "more mature," and variations thereof. The other 80% said, "Like me," or some variation thereof. It turned out to be one of my least productive threads evah.
This is not to say, though, that in particular situations one is never primarily employing Te aspects of oneself, or primarily employing Fi. But rather it is to say that the lessons learned in Te context can be used to teach Fi, and the lessons learned in Fi context can be used to teach Te.