The first instinct is the strongest force in the personality. It is usually where most of our "unexplainable" bad behaviour occurs. We focus on all 3 elements of this instinct.
With the second instinct, we focus on maybe 2 of the 3 elements of it. We sometimes use the strategy of the first instinct to meet the needs of the second instinct. This rarely goes well.
The third (last or bottom) variant in the stack is can be called one's “blind spot”—it is akin to an unused muscle that on occasion feels sore. One believes that this area is uninteresting and unimportant, that one can do without it. At the same time, there is shame associated with the 'blind spot' variant - a sense of deficiency. One constantly feels like one is lacking skills and refinement in the areas pertaining to your last instinct.
Often a negative reaction develops in response to seeing your last instinct operate in others. For example, SP-last people might grow impatient with those who devote a lot of time and effort into making themselves well fed and comfortable - fiddling with the room temperature, checking seat cushions, arranging their bottled water, etc. SP-last people can grow bored if they find themselves trapped in a conversation about food, home decorations or furniture, local deals, home prices, salaries. SX-last people might feel uneasy when they see people openly demonstrating their sexuality, gender orientation or sexual preferences, engaging in PDA, discussing private feelings and experiences, etc. SO-last people might get impatient with 'shallow' socialite chit-chat, get frustrated when required to network, and wonder how others can keep up with so many acquaintances. One takes the dominant instinct as a given and believes that everyone should be this way, hence people become surprised and even frustrated when they meet others who show no concern for their primary area of preoccupation.