Though everyone has Ne/Si, Ni/Se, Fi/Te, and Fe/Ti through primary and shadow functions, as you can see, the order that each pairing comes in can drastically change the individual’s behavior and means of thinking. In fact, really, it’s the order of these pairings that determines the individual’s personality type altogether.
As J. E. Sandoval says, an individual can either lead with a judgment pairing (Fi/Te or Fe/Ti) or a perception pairing (Ne/Si or Ni/Se). Also, an individual can lead with a proactive (Extraverted) function or a reactive (Introverted) function.
“The default state of an individual’s psyche will rest in the primary oscillation pair while the secondary oscillation pair will be supportive and feed the first pair”. However, the secondary pair will only seek to properly aid the primary pairing, it will not pursue aims outside of such. The psyche will draw all of its attention and obsession towards the primary pairing.
If an individual possesses Fi/Te as their primary pairing, they will be lead towards certainty and internal alignment, seeking to make conclusions. Both Fi and Te are judgment functions and though they are starkly different, they require each other in order to make conclusions successfully.
Then, Ne/Si will act as the subordinate process that seeks to aid Fi/Te through delivering data by which Fi/Te can make more refined conclusions. This data will be analyzed by Fi/Te and concluded upon.
A common misconception among many people is that the functions come in different percentages with Fi being in larger quantity for INFPs or Ni being in larger quantity for INFJs. However, this is not true, “the psyche does not work as compartmentalized bits”.
So instead of the arrangement of functions appearing like “Fi > Ne > Si > Te”, instead, it should appear as “Fi(Ne-Si)Te”. In this case, Ne/Si is contained within Fi/Te, and the psyche is lead by reactivity.
For other pairings, the polarity of Introversion vs Extraversion and the polarity of judgment vs perception determines the order of the functions and pairings in each of the sixteen different types.