If you want to understand an introvert you need to understand what his dominant function is. The simple form, not the complicated drawn out form.
This is what drives each -
Ti is introverted thoughts
Si is introverted detail
Ni is introverted concepts
Fi is introverted feeling
How does this work? These are not connected to the outworld without access to external data/judgement. So concepts is what drives dominant Ni. This is their achilles heel. This is what causes them to feel, to think, its a path that steers them.
Ti is thoughts. Our thoughts control us. An ESFP I have known asked me a single question and because of what I said/how I responded was able to understand 90% of what drives me.
Si is detail. They fear the details, they enjoy the details,they push to reach them.
Fi is the same as Ti, but in regards to feeling.
To be able to work with a introvert, where they are going, where they have been, what they fear, what they enjoy you need to understand whether they are Si/Ti/Ni/Fi. When you use Si with Ti they may go down a completely different path. Same if you use Ni with Fi.