Instinctual Stacking: So/Sp
• Sheldon’s interests and (obsessed) acquisition of knowledge are both indicators of being NT and Type 5. Admittedly, being NT and a Theoretical Physicist are a stereotypical combination, but in his case it is rather accurate.
• Sheldon’s Ti subtype is very strong (likely abnormally so), resulting in an abnormally strong “boost” in Si matters and focusing on such; his SP instinct contributes to him being hyper-aware of good food (and its contents), a room’s temperature, and needing the perfect place to sit. Having said all that, Si is not his dominant function. When he became sick, he failed to care for his health properly on his own (besides the fact of being paranoid of becoming sick -> another point for a strong w6 alongside the weaker Si) and required outside help. Additionally, he is known for being unbearable when he is sick, unable to be left alone and provide for himself.
• Sheldon can exhibit quite perfectionistic/OCD behaviour. Being very Ti (and Si) focused (and neurotic 6 wing), he needs to have perfect logical order and finds logically inconsistent statements/actions insufferable.
• Another sign that points towards Sheldon being weak in Fe, but valuing it all the same, shows itself whenever someone confronts him with a socially accepted norm in regards to actions of courtesy. For instance, when Penny told him that giving gifts is a social custom that cannot be dismissed, he readily accepted this and was determined to buy a gift for Leonard, even though he was against doing so before. Also, he prides himself on being able to read other people’s emotions on the rare occasions he manages to do so.
• Sheldon’s SX blindspot is apparent in how he has little interest in close, passionate, romantic relations and rather scorns people who are overly concerned with such. His first instinct is Social, which can be noticed whenever he mentions how he desires to contribute to society in a meaningful/notable way (aka wanting to be nominated for a Nobel Prize), how he values friendship and finds delight in pop culture. It should be noted that being SO first doesn’t imply that one has good social skills, or vice versa.