As I have mentioned a fair amount in previous posts, humans have needs. In some ways, this is obvious. For example, it's clear that if I do not eat, I will die. Yet, it's also true, and not so clear, that if I do not have human connection, I will not live well at best, go insane at medium, and, again, die at worst. (Usually only babies die of lack of connection, but there have been links between life span and social life.)
In the scientifically and materialistically (e.g. atheists) minded communities, it's very common to reduce every issue or behavior to something relating to the desire to survive. However, this isn't a complete view of human life. A simple, but perhaps flawed, example of this is to think about what would have someone jump in front of a bullet for someone else. Another point to consider is what would have humans evolve to think at all. Animals survive fine without thinking, and, in many cases, emoting capacity.
In any case, we as humans have different realms within us. We have the physiological realm of the body and body chemistry that functions mostly without our being aware of it. We have the realm of feelings, where we have emotions. Emotions are also body chemistry, but we can be aware of them. Then we have the realm of thinking. Thinking is also body-related, but is the most superficial, new, and least in control part of our selves. Thinking is fundamentally self-awareness.
Of course, we can be broken down into many different parts, and all parts of the body are interconnected (also the great neuroscientist Damasio says, it's basically impossible to denote where body chemistry's impact on our self-awareness ends and our awareness's impact on it begins), but the reason I do it this way is to discuss fundamental insecurities. The reason I want to discuss fundamental insecurities is because they come up a lot in relationships.
I propose that the fundamental need of our biological self is survival. Therefore, the fundamental insecurity and question of this part of ourselves is safety. Am I safe?
In a relationship, this will come up a lot. You will be with your partner and something they do or say will make you feel fear for your wellbeing. When you feel taken care of, you will feel joy. Therefore, I also propose that the fundamental upsetting emotion of the body is fear and the fundamental comforting emotion of the body is happiness.
You would use this as a practical tool by noticing when you are afraid and pinpointing what is happening in the situation that is making you feel unsafe.
I propose that the foundational need of our emotional self is connection, and the question of "Am I connected?" is the most important for this realm and creates the most insecurity. However, I also believe this is kind of a misnomer, because connection in many cases means an exchange of love, or some kind of loving act. So you could also say the question is "Am I loved?"
Therefore, I believe the fundamental comforting emotion of the feeling part of you is love and the fundamental upsetting emotion is sadness, the sadness you experience when you feel disconnected.
So when you're having an emotional issue that makes you feel sad, you can try to pinpoint what is disconnecting you from your partner and how can you connect back together.
I propose that the fundamental need of our thinking part of ourselves is understanding. Therefore the most basic question and insecurity of our thoughts is "What does this mean?" "What's the point?"
This is both a cosmic issue, meaning that we seem to crave to understand the meaning of life, but also a personal issue in that we don't know what we are doing in relationships, why we want certain things, why someone would want us or the fear that they really don't, that there is something we are missing.
When we do not understand something, we become frustrated, angry. Therefore, I believe the most basic upsetting emotional experience of the thinking part of us is anger, and the most basic comforting emotional experience of the thinking part of us is the "a-ha," or the surprise of new clarity.
So for this as a tool, if you're feeling angry in your relationship, you can try to understand what it is that you do not get about yourself or your partner. What do you not understand about a situation? What question do you have? What do you want to know that you just can't let go of?