According to him, the least likely pairings to succeed are types where the first three letters are different, and the last letter the same. (For example, an INTJ with an ESFJ, or an INTP with an ESFP.)
Why, you might ask? Nardi says despite having judging (J) or perceiving (P) in common, if all the other letters are different, their other personality functions are always competing with each other. How you approach your world (judging vs. perceiving) may be the same, but how you get your energy (introvert vs. extrovert), gather information (sensing vs. intuition), and make decisions (thinking vs. feeling) are all different.
“It’s like every time one person wants to go left, the other wants to go right, in the most confusing or annoying way,” he explains.
In addition to that, Nardi adds that a couple with one SP (Sensing/Perceiving) and one NT (Intuitive/Thinking) typically won’t last as long as an SJ-NF pair (Sensing/Judging and Intuitive/Feeling). “This does not mean less rewarding, just not as long. Why? Both SP and NT types are pragmatic, while SJ and NF are affiliative,” he says, noting that affiliative types “tend to be more focused on or invested in sustaining relationships.”