Ti: No one is more qualified to determine truth than myself.
Fi: No one is more qualified to determine what is morally right than myself.
Not saying that Ti or Fi is egocentric. Saying that’s the mentality. Ti has to rationalize. Fi has to reflect. Ti reflects on logic. Fi reflects on morality.
Neither is a standalone. Perception, sensation, and their respective feeling/thinking function act as a means to balance everything out.
Ti-Fe is likely to believe a person must use reason to consider what is the correct solution. They are likely to believe that the solution based on reason is the morally just one. This goes for Fe-Ti to a much lesser degree since the “common good” is prioritized and the reason is secondary. Fe-Ti might use reason to advocate for the common good.
Te-Fi is likely to believe that a person can discern what is morally correct through objective facts and by reflecting upon individualized principles. They are likely to believe that the best solution is the solution is a solution represented by facts outside of them. Fi-Te has this to a lesser degree. They are no less capable, but they prioritize the “rightness” discovered within themselves. Fi-Te makes appeals to facts in the outside world.
The differences can seem nuanced. When we think subjective principles, we tend to think it’s introverted feeling.
Introverted thinking dominants have a tendency to not prioritize personal feelings at all. They prioritize people’s feelings even when they don’t care about them because, to them, it’s the logical decision. That’s probably why Ti dominants are stereotyped as relaxed and flexible.
I suspect that Fe-Ti/Ti-Fe don’t regularly care about their personal feelings. If they’re feeling something strongly without reason (Ti-Fe) or group principles (Fe-TI) it might be considered a bad thing.
I suspect Fi-Te is the opposite. Fi users can feel alone and misunderstood, but, to them, the best option is to see beyond those things and become the best person they can be. Fe users can dish out this advice, but they have the hardest living by it. Fi users (probably Fi-dominants the most) can have a hard time understanding what they want their place in the world, but that’s their ultimate priority.