The fourth letter of your type code says which mental muscle (of your two favourites) you prefer to use in the outer world. That is, which mental muscle is to the right of the line. To put it another way: when speaking or doing things, do you tend to use your preferred Judgement mental muscle (T or F), or your preferred Perception mental muscle (S or N)?

A preference for using the Judgement mental muscle in the outer world often leads to a planned and organised lifestyle. A preference for using the Perceptive mental muscle in the outer world often leads to a flexible lifestyle that goes with the flow. Bad Joke: An airline planned it's flights to the last detail so that no human intervention was required. This system reassured passengers greatly, until on one flight a standard announcement message said "you are now being flown at 30,000 feet by the most automated system in the world. We can assure you that nothing can go wron... can go wron... can go wron... can go wron..."